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| radiometrix ltd, m48a-433-usx2 modem manual page 1 figure 1: m48a-433-usx2 the m48a is a simple, half duplex, transparent data link device. it provides a basic 4800 baud rs232 compati ble path without the user needing to format, code, dete ct or otherwise worry about modifying his existing datast ream or providing extra 'control' lines. the user interface datarate, addresses and operating parameters can all be easil y re- programmed via the serial port. it ought to be emphasised that the m48a is a very s imple, easy to use, device. as supplied, it operate s as a 4800 baud, transparent half-duplex data link. if re quired, there is an extensive range of programming options, allowing user interface speed from 1200 to 76800 baud, hardware flow control, one to one, one to many and broadcast addressing options, and acknowle dge/re-transmit error handling protocols. simple st ore and forward repeater operation is also provided. a good demonstration can be had by connecting a pai r of pcs by their serial ports and a null-modem cab le, and setting up terminal emulators (4800 baud, async hronous, local echo on) on both computers. confirm that good rs232 communication is present, and then replace the cable with a pair of m48a modems. the resulting 'radio teletype' can be entertaining to p lay with. features usable range over 1km (@ 100mw rf power) up to 100mw rf power output: adjustable via serial command 128 serial select channels 5kbps pulse duration coded protocol synchronisation codes and checksum to reduce false triggering on noise programmable transmit address and four receive addr esses programmable timing parameters (preamble length, et c) programmable auxiliary serial output (to program ra dio modules) programmable serial modem baud rate (1200 - 76800 b ps, half-duplex) addressable point-to-point and point to multi point packet acknowledge/resend (ack) mode store and forward repeater function applications pdas, organisers & laptops handheld / portable terminals remote operated vehicles data loggers in-building environmental monitoring and control industrial (scada) telemetry and m2m systems fleet management, vehicle data acquisition the M48-433-USX2 presents m48 modem ic combined with a usx2 radio module and suitable interface circuits, power supplies, connectors to provide a complete rs232 radio modem interface. optionally, the board can be housed in an eas80 extruded aluminium housing. in the simplest case, a pair of these units (with suitable aerials and powe r supplies connected, of course) can be connected directly to the serial ports of a pair of industria l pcs and the resulting wireless data link used without any further installation or programming. uhf nbfm multi channel rs232 radio modem issue 1, 29 october 2012 hartcran house, 231 kenton lane, harrow, middlesex, ha3 8rp, england tel: +44 (0) 20 8909 9595, fax: +44 (0) 20 8909 223 3, www.radiometrix.com m48 - 433 - usx2
radiometrix ltd, m48a-433-usx2 modem manual page 2 user interface 1 5 9 figure 2: db9f rs232 connector pin arrangement pin description pin name i/o function 1 rx_flow out rs232 'dcd' output. active (+ve leve l) when data is present in rx buffer 2 rx_data out rs232 'rxd' data out 3 tx_data in rs232 'txd' data in 4 rx_hold in rs232 'dtr' input. take -ve to inter rupt rx data output 5 0v - ground 6 enable in rs232 'dsr' pull low to enable unit. (internal 20k pullup to vraw) 7 n/c - (rts pin on standard rs232) 8 tx_flow out rs232 'cts' output. active (+ve level ) when the tx buffer is nearly full 9 +5v out out regulated supply output. 500ma max. ( switched by pin 6) jumpers lk 1. link to hold unit permanently on (disables p in 6 switching) lk 2. link to enable rx dataflow inhibit (dtr) in put. as supplied, all links are open power this is a 2.1mm power connector. center pin is po sitive. supply requirements are: 6-15v normal operation notes: 1. all input pins will tolerate true +/- rs232 l evels. no buffering is required. 2. the modem provides a half duplex link: provide d no two devices attempt to transmit at one time (a 'high' on rx_flow may be used as a primitive 'othe r user on channel' indication) no further restrictions on data transmission need be made, as all transmit timing, valid data identification and datastream buffering is conducted by the unit. ther e is no 'transmit enable' pin. sync and framing words in the packet prevent the receiver outputting garbage in the absence of signal or presence of interference 3. if the user interface rate has been set to gre ater than 4800 baud, then the modem cannot empty th e 128 byte tx data buffer as quickly as the user can fill it. in this case it is either necessary to lim it the average data throughput, or to monitor the tx_flow (cts) output, and interrupt the dataflow when this pin signals a full buffer. tx_flow activates when the buffer is 3/4 full , and deactivates when it is empty 4. a fairly complex addressing structure is inclu ded in the datastream. units have four independent (or'ed) receive addresses and a separate transmit a ddress. (all units are supplied set to tx address =1, rx addr1 = 0, rx addr2-4 = 1) note: for details relating to the radio module fitt ed on board, see usx2 datasheet http://www.radiometrix.com/files/additional/usx2.pd f radiometrix ltd, m48a-433-usx2 modem manual page 3 condensed specifications frequency 433mhz or 458mhz frequency stability 2.5khz channel spacing 25khz number of channels 1 of 128, user programmed supply voltage 6 - 15v current 140ma transmit (100mw) 32ma receive / idele(plus up to 20ma into rs232 po rt) operating temperature -20 to +70 c (storage -30 to +70 c) size board version: 80 x 56 x 18mm (excluding connector s) eas version: 83 x 64 x 30mm (excluding connectors) (case is an eas80, silver from evatron) spurious radiations compliant with en 300-220 interface user 9 pin d type power 2.1mm connector rf sma indicators transmitting (red led) intended approval etsi en300-220 (aus/nz version available) transmitter output power 100mw (+20dbm) +/- 1db (user programmable in 1db steps to -10dbm) 458mhz band allows full 100mw 433mhz (eu) permits 10mw 433mhz (aus/nz) permits 25mw tx on switching time <50 ms (from txe transition) modulation type fsk (f3d) deviation +/- 3khz adjacent channel tx power -37dbm tx spurii -45dbm inputs data (cmos/ttl compatible) receiver sensitivity -113dbm for 0.1% data error image / spurious -60db blocking -85db spurii, adjacent -60 db lo re-rad <-60dbm modem baud rate 4800 baud (transparent, half duplex) format 1 start, 8 data, 1 stop, no parity radio channel data rate 5.1 kbit/sec peak (maximum transmitted frequency: 3.2khz) coding variable period phase coded packet length 1-16 bytes addressing 1 of 254, user programmed. multiple rx addresses buffers 128 byte tx, 64 byte rx flow control cts, dcd and dtr radiometrix ltd, m48a-433-usx2 modem manual page 4 application information what can you do with an m48a ? the m48a is a 4800 baud radio modem, compatible wit h narrowband radios. just a faster i1200, or a simpler rpm1 ? ....... no t quite. what does an m48a do ? in the simplest possible sense, the m48a is just a radio modem baseband device. it provides an interface between a user's asynchronous (?rs232 typ e?) serial port and the audio channel of a low power radio module. the m48 will transparently handle a half duplex se rial stream at 4800 baud, buffering framing and cod ing the data into a baseband signal that a narrowband w ireless module can handle. at the receive end it decodes the audio signal back into serial data. the timing requirements of the radio are allowed for w ith internal fifo buffers, while the noisy imperfect ra dio baseband path is hidden from the user behind s/ n efficient bit coding and data packetisation, with frame synchronisation and a crc error detection protocol. the interface an m48 can be used with just two serial data lines (txd, rxd). in many applications that is sufficien t. if data is being sent in both directions (half-duplex) however, it is necessary to allow for the turnarou nd time (transmit to receive or vice versa) as the m48 cannot handle transmit data input while it is deco ding receive data. (also, in advanced modes, such as whe n user interface data rate is higher than 4800 baud (see later), then transmit data hand-shaking is nee ded) in these cases it is useful to have more informati on as to the status and timings of the link. the m4 8 provides additional 'handshaking' lines: rx flow. goes 'high' when the device has valid data to output (?dtr? out) tx flow. high when the transmit buffer is ? full, l ow when empty (?cts? out) rx hold. when pulled low, prevents device from outp utting data (?rts? in) buffers as alluded to earlier, data into and out of the m4 8 is buffered through a pair of small fifos. on the transmit path a 128 byte buffer is used, while on r eceive a 64 byte buffer is implemented. these buffe rs actually occupy the same memory space on-chip, so t he part cannot receive and output serial data . transmit operations will always over-ride receive. a byte sent to the device will clear the receive bu ffer, even if it contains valid data. (an algorithm which reads the 'rx flow' signal can prevent this occurr ing) in simple, transparent mode these buffers are invi sible to the user. speed in normal usage the m48 uses a 19.6608mhz crystal for a basic 4800 baud transparent throughput. however, elementary communication theory tells us t hat ultimate range and s/n performance (sensitivity) relates to bandwidth, and hence data rate. in applications where ultimate range matters more than a fast data path the m48 can be fitted with slower clock crystals. in these cases the fundament al link data rate is reduced (and other timing parameters scaled accordingly) but the link range w ill be increased. crystal frequency 19.6608mhz data rate 4800 baud sensitivity +0d b 9.8304mhz data rate 2400 baud sensitivity +3db 4.9152mhz data rate 1200 baud sensitivity +5db 2.4576mhz data rate 600 baud sensitivity +7db [ slower clock frequencies will also allow operatio n on lower power supply voltages than the basic +5v normally specified, see microchip pic16f648a data s heet for more information ] radiometrix ltd, m48a-433-usx2 modem manual page 5 radio interface the raison d'tre of the m48 device is to insulate the user from the peculiarities and limitations of the radio module's audio path. while a detailed analysi s of the over-the-link signals is not intended, a basic overview may be useful: three signals connect the modem chip to the radio: tones_out, tones_in and n_txe. all are digital levels (so connection must be made to the digital baseband pins of the radio, not the low level analogue connections). at the bit-level the radio link signal generated b y the m48 is a proprietary biphase (synchronous) bitstream with a maximum frequency component of 3.2 khz. there is a pseudo-random data whitening function applied to the data, but the code still do es not have a perfect 50:50 mark space balance, so should be considered a dc coupled signal. at the r eceiver end a conventional averaging data extractor will function but a quasi-dc coupled (peak detectin g) type, such as the radiometrix qr96, will give optimum performance. the data stream is further formatted into packets. each packet contains a framing sequence, address and status information, a crc and 1-16 data payload bytes. transmitter on-time delay is allowed for by the addition of a preamble sequence, while during c ontinuous data transmission the packets are transmitted end-to-end. [ unless otherwise programmed, all units send on ad dress 1 and receive on address 0 (broadcast) and address 1 ] m48 also has an auxiliary serial output (only) pin, which is used to allow the user to send serial pro gramming strings to the associated radio module through the device. programming the m48a in the simplest case an m48 can be used 'as supplie d' as a straight forward transparent data link. the re are, however, a number of further options and features w hich require the user to program parameters into th e device. normal transparent data mode is referred to as 'dat a' mode. to program the device, it is necessary for it to be in 'setup' mode. the device is programmed through the rs232 port (wi thout needing extra 'pgm mode' switching pins or extra hardware). the command set uses simple readab le ascii words, and decimal or hex numbers. all commands are in upper case. when in setup mode the usual radio data communicati on functions are suspended, but limited one-packet- at-a-time non-transparent operation is possible, vi a special commands. the setup mode is activated by means of a 'break / respond' protocol entering setup : user generates a 'break' (long 'space' cond ition) m48 sends two char acters, an @ and a random printable ascii character user sends back th e random character m48 replies with a login message ?m48 setup? and enters setup mode there is a 5 second timeout following the break wit hin which the response must be sent , or the device reverts to data mode. an ascii 1 (ctrl a) resets t he timeout and generates a new @ and random charact er sequence. [ 'break' conditions can be generated in several wa ys. some terminal emulators have alt or ctrl key sequence. dedicated hardware can be used to force a long (50-100ms) logic zero onto the txd pin. or a n ascii zero can be sent at a much lower baud-rate ] once in setup mode, input bytes are stored in a 32 byte (maximum) command buffer and echoed back to th e serial output. space characters are echoed back, bu t are not loaded into the buffer. commands are either short words or single command c haracters. (for example, a radiometrix ltd, m48a-433-usx2 modem manual page 6 the unit will only respond to certain command strin gs: upper case characters are used for all commands spaces are echoed, but are ignored by the parser single character command commands ascii function enter 13 processes the input buffer contents (and clears the buffer) escape 27 terminates setup mode and returns to normal 'dat a' operation ? 63 prints the current contents of the command buffe r / 47 (as above) - 54 shortcut for the state command (see later) & 38 shortcut for the rx command delete 127 clears the input buffer general commands commands function default the unit self-reprograms with all original factory preset values state prints out the current operating parameters (a sing le minus sign, ascii 54, does the same) lock the unit now defaults to setup (rather than data) m ode on power up exit return to data mode (same effect as an escape (asci i 27) byte) if a lock command is in force, an escape byte has n o effect, but exit overrides lock test turns on the transmitter, and outputs a continuous 200hz tone this mode is disabled by any activity on the txd in put rx turn on the receiver/decoder (as if in data mode) and output received packets as normal this mode is disabled, and command mode re-entered, by any activity on the txd input baud rate commands as supplied, the main interface is set to 4800 baud , and the auxiliary port to 2400 baud . commands function notes baud b1 set main port baud rate b1, b2 are baud rates baux b2 set aux port baud rate only the first two digits ar e needed, i.e. baud 12 is valid main port (b1) supports 1200, 2400, 4800, 9600, 192 00, 38400, 57600, 76800 aux port (b2) supports 1200, 2400, 4800, 9600 on ly these setup parameters are immediately stored in e2 prom, and take effect right away. remember that baud rate scales with changes in crystal frequency (for example, if a 4.9152mhz crystal is fitted then baud 2400 will set a baud rate of 600). when the interface baud rate is higher than the (48 00 baud nominal) radio link interface speed, the sy stem is no longer truly transparent. as the modem is removi ng bytes from the buffer slower than the user inter face is supplying them, it is possible to over-fill the buf fer and lose data, unless the user carefully contro ls the timing of the data stream or uses the tx_flow signal. this pin allows the status of the transmit buffer t o be monitored. it begins low. it goes high when th e buffer reaches ? full, and is then re-set (to low) when th e buffer is empty again. it can be used to provide a simple 'cts' signal. [ it is possible to 'lose track' of the baud rate o f a unit while manually programming it. in this cas e an easy way of 'finding' the speed can be used: a byte shou ld be sent to the device at each of the valid baud rates, and the echoed character monitored. only at the cor rect rate will a correct echo be seen ] timing commands commands function delay dd set the initial delay between first byte arrival an d transmit start (20ms default) pream pp set the number of (620us long) preamble bits (80 bi ts / 50ms default) txoff oo set the tx ramp-down period (20ms default) note : variables dd, pp and oo are all two digit hexadec imal values (00 to ff). these timing parameters are immediately stored in e2prom, and take effect right away. radiometrix ltd, m48a-433-usx2 modem manual page 7 the timing commands directly affect the way the mod em device controls the radio module. beware! if the y are set incorrectly then data errors or unreliable operation will result. the default settings are a safe, conservative setup for a typical 50ms set-up time multi-channel trans ceiver. for faster (usually single channel) radios the prea m value can be reduced. do not reduce this paramete r too far, as it must deal with the settling times of the receiver data recovery circuit as well as the transmitter turn-on time. the delay and txoff parameters are primarily concer ned with optimum channel usage with intermittent user data streams. delay is a duration between fir st byte received (into an empty buffer) and the transmitter key-up, while txoff holds the transmitt er on after a packet has finished sending. if a user is controlling their serial data stream m ore closely, and sending data in discrete, well org anised bursts, then delay and txoff can be set to zero. addressing the m48 data packet includes an address byte. it wi ll only communicate with a unit set to the same add ress. there are four receive addresses (of which adr1 is usually set to zero as a 'broadcast' mode) and a separate transmit address. multiple receive addresses can be useful for multip le node systems, and for setting up simple (manual routing) repeater networks commands function adr1 aa set receiver address 1 adr2 aa set receiver address 2 adr3 aa set receiver address 3 adr4 aa set receiver address 4 adtx aa set transmitter address addr aa set rx address 1 to zero and set tx address and rx addresses 2, 3 and 4 to a notes : 1. aa is a two digit hexadecimal value (00 to fe). address ff (255) is not permitted. 2. address commands write to volatile memory. to tr ansfer programmed addresses to the power-up settings, the prom command must be used. 3. as supplied: adr1 is zero, and adr2, adr3, adr4 and tx address are all set to 1. mode commands beyond it's usual 'transparent data' mode, the m48 can also operate in an 'extended' mode. in this ca se the maximum packet size is reduced from 16 bytes to 14, and a 'burst identifier' word is included (obvious ly this slightly reduces overall throughput). on transmit, a different burst identifier is attach ed to each new packet. the receiving unit ignores t he second (and subsequent) packet with the same identifier. t his allows a receiving m48 to ignore multiple copie s of the same data packet (as will be encountered in mul tiple transmission or repeater/network systems) commands function mext extended mode (burst id on, multiple transmissions set by tries) akn the unit now operates in acknowledge/resend (extend ed) mode tries rr number of transmissions attempts allowed in akn and mext modes timeout tt duration of akn resend timeout (tt x 0.41ms) staf operate as a store and forward repeater (with mext set, or not) notes : variables rr and tt are all two digit hexadecimal values (00 to ff) extended mode (mext) is used with repeater systems. with tries set to two or more, this mode sends each packet several times (increasing the chance of reception at extreme range). lastly, the m48 has an ' akn/re-transmit ' mode. in this case, after each packet is sent, the receivin g unit sends back an knowledge message. if this message is not successfully decoded, at the transmitting end, it will re-send the packet. the knowledge timeout peri od and the number of permitted re-tries are both us er programmable. [ do not use akn mode with staf repeaters. timing c onflicts occur ] akn mode provides the greatest data transfer reliab ility, although the overall data throughput is mark edly reduced. radiometrix ltd, m48a-433-usx2 modem manual page 8 commands function norm the unit returns to standard, transparent mode prom writes the current volatile settings (addresses and operating modes) into the e2prom as the new power-on settings default the unit self-reprograms with all original factory preset values diag enter a diagnostic mode, where the address, length, checksum and decoder status byte for every received burst are printed additional info on the m48 diag mode takes effect when returning to data mode (an exit o r radiometrix ltd, m48a-433-usx2 modem manual page 9 timings the data throughput of the m48a is limited by the r adio path. in continuously streaming (transparent) mode a baud rate of 4800 baud is supported without any buf fer overflows. byte latency is influenced by the switching perform ance of the radio (and the programmed delay and pream values). in default mode (20ms delay, 50ms preamble) the sin gle byte in to out latency is of the order of 110ms (20+50+40ms burst length and processing delays) alt hough in streaming data this is reduced to around 30ms if radio switching times are faster, then the pream ble duration and the tx off delay can be reduced (c rystal controlled radios such as nim2 work well with 15ms of preamble, 5ms tx off) and latency falls to aroun d 40ms in ank mode, the switching speed of the radios, and the time absorbed in sending and decoding the acknowledge burst dominate the data throughput. th e acknowledge in itself requires only 20ms, but the requirement to switch both radios between receive a nd transmit (to send the data packet, and then the akn packet) adds a significant overhead. referring to the default timing setup this results in 1 packet per 150ms, and a peak data throughput o f only 900 baud, although if radios with faster switching performance are used then this is significantly inc reased. (with nim2 or bim1 radios, the preamble duration ca n be significantly reduced, and an acknowledged mod e data rate of well over 1200 baud is achievable) unless only short data bursts are used, we recommen d the use of cts flow control if akn is selected rs485 to rs232 adaptor figure 3: rs485 to rs232 adaptor connections m48 applications board can be supplied with rs232 d b9f, 2.1mm dc jack connectors replaced with 3-wire rs485 to rs232 adaptor and power terminal blocks. http://www.ti.com/lit/ds/symlink/ds3695.pdf jumper link jp13 is provided for 120 termination. usb-rs485-we-1800-bt adaptor cable can be used to e valuate m48 rs485 application board on a pc/laptop running hyperterminal terminal emulation program via virtual com serial port. http://www.ftdichip.com/products/cables/usbrs485.ht m http://www.hilgraeve.com/hyperterminal/ radiometrix ltd, m48a-433-usx2 modem manual page 10 figure 4: rs485 to rs232 adaptor schematic ordering information part no. description frequency band M48-433-USX2-eas usx2 version in extrusion case ch0 :433.05 ? ch69:434.775mhz M48-433-USX2 usx2 version as board ch0:433.05 ? ch6 9:434.775mhz when ordering rs485 radio modem application boards, -rs485 suffix should be added above part numbers radiometrix ltd hartcran house 231 kenton lane harrow, middlesex ha3 8rp england tel: +44 (0) 20 8909 9595 fax: +44 (0) 20 8909 2233 sales@radiometrix.com www.radiometrix.com copyright notice this product data sheet is the original work and co pyrighted property of radiometrix ltd. reproduction in whole or in part must give clear acknowledgement to the copyright owner. limitation of liability the information furnished by radiometrix ltd is bel ieved to be accurate and reliable. radiometrix ltd reserves the right to make changes or improvements in the design, specification or manufacture of its subassembly products without notice. radiometrix lt d does not assume any liability arising from the application or use of any product or circuit descri bed herein, nor for any infringements of patents or other rights of third parties which may result from the u se of its products. this data sheet neither states nor implies warranty of any kind, including fitness for any particular application. these radio devices ma y be subject to radio interference and may not function as intended if interference is present. we do not recommend their use for life critical applications. the intrastat commodity code for all our modules is : 8542 6000. r&tte directive after 7 april 2001 the manufacturer can only place finished product on the market under the provisions of the r&tte directive. equipment within the scope of the r&tte directive may demonstrate compliance to the essential requirements specified in article 3 of the directive, as appropriate to the particula r equipment. further details are available on the office of comm unications (ofcom) web site: http://www.ofcom.org.uk/ information requests ofcom riverside house 2a southwark bridge road london se1 9ha tel: +44 (0)300 123 3333 or 020 7981 3040 fax: +44 (0)20 7981 3333 information.requests@ofcom.org.uk european communications office (eco) peblingehus nansensgade 19 dk 1366 copenhagen tel. +45 33896300 fax +45 33896330 ero@ero.dk www.ero.dk |
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