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| Hartcran House, 231 Kenton Lane, Harrow, Middlesex, HA3 8RP, England Tel: +44 (0) 20 8909 9595, Fax: +44 (0) 20 8909 2233, www.radiometrix.com M48A MODEM PRELIMINARY 07 September 2009 M48A modem chip - for narrow band wireless data link The M48A is a half-duplex serial modem controller suitable for use with narrow band receivers, transmitters and transceivers. It supports a maximum transparent data throughput of 4800baud while baseband modulation frequencies do not exceed 3.2KHz. The device supports (programmable) long startup/preamble durations sometimes required for synthesized narrow band devices. Figure 1: M48A-000-DIL modem IC The M48 provides a half duplex link, but provided no two devices attempt to transmit at one time (a 'low' on RX_flow may be used as a primitive 'CTS' indication) no further restrictions on data transmission need be made, as all transmit timing, valid data identification and data stream buffering is conducted by the device. This unit supports a range of user interface data rates, in asynchronous data format: 1 start bit, 8 data bits, 1 stop bit. The supplied default (and the maximum transparent throughput) is 4800 baud To connect to a true RS232 device, inverting level shifters must be used (MAX232 type are ideal, but simple NPN transistor switches often suffice). With typical microcontrollers and uarts, direct connection is usable. Note that TXD has no internal pullup. Features ! ! ! ! ! ! ! ! ! ! ! ! ! Operating voltage (temperature): 5V for standard version (-40C to +85C) Maximum usage of the range capability of an RF module Compatible with fast or slow transmitter power up timing requirements 5kbps pulse duration coded protocol Synchronisation codes and checksum to reduce false triggering on noise Programmable transmit address and four receive addresses Programmable timing parameters (preamble length, etc) Programmable auxiliary serial output (to program radio modules) Programmable serial modem baud rate (1200 - 76800 bps, half-duplex) Suitable to be used with Narrow Band FM radio modules 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 Radiometrix Ltd M48A Modem Data Sheet page 1 User Interface M48A is an 18pin PIC16F648A, running proprietary software. It requires a 4.5v minimum supply. Aux out LAMP TXE RST Vss (0V) TX FLOW RSTXD RSRXD RX FLOW 1 2 3 4 5 6 7 8 9 18 17 16 15 14 13 12 11 TONE OUT TONE IN OSC1 OSC2 Vdd (+5V) RX Inhibit Figure 2: package type, 18-Lead Plastic Dual In-line (PDIP - 300mil wide body) Pin description: Pin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Name AUX OUT LAMP TXE RST 0V TX FLOW RSTXD RSRXD RXFLOW DFLT_0 DFLT_1 TX inhibit RX inhibit Vcc OSC2 OSC1 TONE IN TONE OUT I/O out out out in supply out in out out in in in in supply out in in out Function Serial output to radio module (1200/2400/4800/9600 baud true RS232) High when in transmit Low = enable transmitter Drive low to reset device. Otherwise pullup to Vcc Supply ground Low indicates tx buffer near full (3/4 full) Inverted RS232 datastream in Inverted RS232 datastream out Low indicates data received or in rx FIFO buffer Default timing set Default timing set high = normal mode, low = inhibits transmit (data in still goes to buffer) high = normal mode, low = prevents serial data being output 5V (regulated power supply); Decouple with 100nuF close to IC Connect to 19.6608MHz crystal via 100 resistor Connect to 19.6608MHz crystal Baseband input from receiver data output Baseband output to transmitter data input NOTES: 1. M48 is intended for use with USX/UHX, RMX and LM series radios. If other radios are used, then to reliably recover the data format an external peak sampling data recovery circuit is recommended, such as QR96. 2. All conncetions are 5v cmos logic level except TXE, which is a an open drain (but do not exceed +5v on this pin) 3. Some Radiometrix transmitters require 3v logic levels on their transit data inputs: In such cases a divider (4K7 series, 10K to ground) on the RXD pin is needed 4. In RX operation, Tone_out becomes a high impedance 5. After pulling TXE low (active), the coder allows about 50mS for TX to power up and settle (this, and other timings, can be modified via the setup mode) 6. RSTXD (pin 7) has no pullup. If the device is only used for transmit, then tie this pin to VCC 7. Vcc must be a 5v regulated supply (4.5 - 5.5v). At this oscillator frequency the pic will not operate reliably at 3v 8. An approximately 5.1kbps multiphase coded comms protocol is used 9. Without external loads the chip draws less than 5mA from 5v 10. tx_FLOW goes low when the tx buffer is 3/4 full. it returns to high state when the buffer is empty 11. rx_FLOW goes low whenever valid data is present in the receive buffer. 12. A simple addressing structure is included in the datastream. Units may be programmed onto one of 254 addresses Radiometrix Ltd M48A Modem Data Sheet page 2 Address 0 is a broadcast 'all units' address Address 255 is reserved (Units are supplied set to adr1 = 0, adr2,3,4 and adr_tx =1) 13. OSC1, 2 require a 19.6608MHz fundamental mode crystal, a series 100 ohm resistor from OSC2, and a pair of 15pF caps : from the crystal pins to 0V 14. DFLT0 DFTL1 high high : slow timing (20mS, 50mS, 20mS) low high : tba high low : tba high high : tba These pins have internal pullups. They are only read at power-up, if the unit has not been already programmed. They are also read on execution of a DEFAULT command 15. TX_inhibit is only sampled as the transmitter is initialising (and before a carrier is being emitted). It is ignored during constantly streaming data (ie: once the transmitter has activated) The Radio / datastream interface A 128 byte software fifo is implemented on transmit (64 bytes on receive). At the transmit end this is used to allow for the transmitter start up time (nominally 50mS), and to buffer data where the user interface baud rate is set to more than 4800 baud. On receive it buffers arriving packets to the constant output data rate. All timing and data formatting tasks are handled by the software. The user need not worry about keying the transmitter before sending data: the link is entirely transparent. For transmission across the radio link data is formatted into packets, each comprising up to 16 bytes of payload data, a framing/sync code, an address byte and a checksum. A simple P/N based scrambler algorithm is applied to the data payload, to 'whiten' the data, although the data stream is not guaranteed to have a strictly 50:50 mark space. A peak sampling data recovery circuit (such as QR96) is recommended In transparent (normal) mode the entire 16 bytes of payload are used for data. In this mode, data can be streamed at 4800 baud (or slower), without restrictions. The unit has, however, other "expanded" modes. In expanded mode, the normal address byte is set to FF, and the first two bytes of the payload contain an address byte and a mode byte, followed by up to 14 bytes of data. The mode byte operates as a special function code (80-FF) or a burst identifier (01-7F). It is never a zero. Burst identifier is an arbitary number incremented after each transmission. It is used to prevent the reception of multiple copies of the same burst when in AKN or repeater operation If less than 16 bytes are in the transmit end fifo then a shorter packet is still sent. When the transmit end fifo has completely emptied, then the transmitter is keyed off. A link latency (first byte in to tx to first byte out of rx) of about [ preamble period + 40mS ] is achievable.. Transmit operations have precedence over receive. If a byte is received on the TXD pin the unit immediately switches into transmit mode, and any data in the the receiver buffers is lost. (for LBT applications this precedence can be modified by using the N_TX_inhibit input) To prevent un-necessary transmission of short packets, a programable delay (usually 20mS) is applied between the arrival of a byte on TXD and the unit commencing it's transmit sequence. Unfortunately, during this delay period, the receiver decoder functions are off-line and data already in the rx buffer is still lost. Raw data is not fed to the radios. A coding operation in the transmit software, and decoding in the receiver, isolate the AC coupled, potentially noisy baseband radio environment from the datastream. Radiometrix Ltd M48A Modem Data Sheet page 3 Programming the M48 In order to use all the functions embedded in the M48, the user must be aware of the setup/programming facility, which allows user customisation of the device's operating modes. The device is programmed through the same RS232 port that is used for sending/receiving data. An RS232 terminal emulator (such as Aterm or HyperTerminal) is an ideal tool. To enter program mode, a 'BREAK' character (a long 'space' condition that triggers a stop bit framing error in the UART) must be sent to the unit. The unit then 'replies' with an @ character, followed by a random character (ascii code between 48 and 79). The user must then send this random value back to the unit within a five second timeout period (after which the M48 reverts to normal operation) Reception of a CTRL-A (ascii 1) will cause a new random value to be calculated and another @ and random sequence is output (and the timeout counter is reset) On reception of the correct byte, the M48 enters `command' mode and sends the string "M48 SETUP" In command mode the radio link is disabled, but characters sent to the unit (at the programmed baud rate, as normal) are echoed back on the RXD pin. The unit will only respond to certain command strings: Upper case characters are used for all commands Spaces are echoed, but are ignored by the parser Keyboard entry COMMANDS carriage return (ascii 13) Escape (ascii 27) ? or / (ascii 63 or 47) - (ascii 54) & (ascii 38) delete (ascii 127) FUNCTION processes the input buffer contents (and clears the buffer) terminates setup mode and returns to normal 'data' operation prints the current contents of the input buffer shortcut for the STATE command shortcut for the RX command clears the input buffer Address setup These commands set up the addresses. An M48 will only communicate with a unit set to the same address. The M48 supports four receive addresses (of which ADR1 is usually set to zero) and a separate transmit address COMMANDS ADR1 aa ADR2 aa ADR3 aa ADR4 aa ADTX aa ADDR aa FUNCTION set receiver address 1 set receiver address 2 set receiver address 3 set receiver address 4 set transmitter address set rx address 1 to zero and set tx address and rx addresses 2, 3 and 4 to aa Notes: 1. aa is a two digit hexadecimal value (00 to FE) 2. Addresses are stored in volatile memory. 3. On power-up the M48 reverts to the defaults in EEPROM (as supplied these are tx addr=1, rx addr1 = 0 and rx addr 2-4 =1) Radiometrix Ltd M48A Modem Data Sheet page 4 Operating mode setup COMMANDS DIAG MEXT AKN STAF NORM PROM MEXT is used for multiple packet send operations, and (with TRIES set to one) to communicate with repeater networks. This mode enables extended 14 byte packet format with burst identifier handling, but without AKN burst generation" It also allows listening in on AKN mode packets, without generating AKN transmissions. In extended mode the data throughput is slightly reduced, as only 14 bytes are sent per packet. Fully transparent 4800 baud operation is not supported. STAF initialises the "store and forward" repeater mode. In this mode, when a packet is received it, it is buffered and re-sent immediately. Care must be taken by the user to control overflow issues when using the store and forward mode, as the repeater only has a 16 byte (one packet) buffer, and cannot re-send two consecutive packets (We recommend setting the TXOFF delay on the sending unit to a time greater than a burst length, so permitting the repeater to clear it's buffer before the next packet can arrive. DELAY should also be set so as to maximise the length of each transmit packet) STAF can be used in extended (MEXT) mode, in which case multiple reception of the same burst by the recipient (via repeater, and direct from sender) is handled by the embedded burst id code (and the same tx and rx addresses are programmed into all units) Alternatively (in normal mode) by manually setting the repeater's transmit address / recipient receive address and sender's transmit / repeater receive to different values, the recipient can be made to respond only to packets from the repeater. Timing and baud rate setup Take great care when setting timing parameters and baud rates. It is possible to upset the correct operation of the unit, or lose communication with it altogether. In the worst case, where an unknown BAUD rate has been set, then remember that the character following a 'break' is always an ascii 64 (the @ character) and that on a scope this easily allows the bit-period to be measured As supplied, the M48 is set to 4800 baud main interface, and 2400 baud on the aux-port These setup parameters are immediately stored in EEPROM, and take effect right away. COMMANDS BAUD b1 BAUX b2 FUNCTION Set main port baud rate set aux port baud rate NOTES b1, b2 are baud rates Only the first two digits are needed, i.e. BAUD 12 iss valid Main port (b1) supports 1200, 2400, 4800, 9600, 19200, 38400, 57600, 76800 Aux port (b2) supports 1200, 2400, 4800, 9600 only COMMANDS DELAY dd PREAM pp TXOFF oo TRIES rr TIMEOUT tt FUNCTION Set the initial delay between first byte arrival and transmit start (20mS default) Set the number of (620uS long) preamble bits (80 its / 50mS default) Set the tx ramp-down period (20mS default) Number of transmissions attempts allowed in AKN and MULT modes Duration of AKN resend timeout (tt x 0.41mS) Note: Variables dd, pp, oo, rr and tt are all two digit hexadecimal values (00 to FF) Radiometrix Ltd M48A Modem Data Sheet page 5 General commands COMMANDS DEFAULT STATE LOCK EXIT TEST RX FUNCTION The unit self-reprograms with ALL original factory preset values Prints out the current operating parameters (a single minus sign, ascii 54, does the same) The unit now defaults to setup (rather than data) mode on power up Return to data mode (same effect as an escape (ascii 27) byte) If a LOCK command is in force, an escape byte has no effect, but EXIT overrides LOCK Turns on the transmitter, and outputs a continuous 200Hz tone This mode is disabled by any activity on the TXD input 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 A Carriage Return ' 'String' commands There are special commands which allow whole strings of characters to be sent via the transmitter, or the auxilliary serial port (usually connected to the radio module programming input) Auxilliary port output (to allow programming of an attached radio module) [ (1-30 byte data string) ] pin [ (1-30 byte data string) Special `transmit a packet from command mode' function. $ (length byte) (1-16 byte data string) ($ is ascii 36) This function output a data packet to the transmitter, then returns to setup mode. `Length byte' is a single hex character. It sets the length of a transient data buffer (the actual buffer length is one more than the value of length, so 0-F corresponds to a buffer between 1 and 16 bytes long) After the length byte, the M48 sends back a colon character (ascii 58) `data string' is a string of bytes equal in number to length+1 When the final byte is received, the modem goes into transmit, and sends a packet Note: By careful use of the & and $ command bytes, the M48 can be used in a non-transparent mode, without ever leaving command mode. This is especially useful for the master node in point to multi-point operation. Timings The data throughput of the M48 is limited by the radio path. In continuously streaming (transparent) mode a baud rate of 4800 baud is supported without any buffer overflows. Byte latency is influenced by the switching performance of the radio (and the programmed DELAY and PREAM values). In default mode (20mS delay, 50mS preamble) the single byte in to out latency is of the order of 110mS (20+50+40mS burst length and processing delays) although in streaming data this is reduced to around 30mS Radiometrix Ltd M48A Modem Data Sheet page 6 If radio switching times are faster, then the preamble duration and the tx off delay can be reduced (crystal controlled radios such as NiM2 work well with 15mS of preamble, 5mS tx off) and latency falls to around 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. The acknowledge in itself requires only 20mS, but the requirement to switch both radios between receive and 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 througput of only 900 baud, although if radios with faster switching performance are used then this is significantly increased. (With NiM2 or BiM1 radios, the preamble duration can be significantly reduced, and an aknowledged mode data rate of well over 1200 baud is achievable) Unless only short data bursts are used, we recommend the use of CTS flow control if AKN is selected Ordering Information: M48A-000-SS - Shrink Small Outline M48A-000-SO - Small Outline M48A-000-DIL - Plastic Dual In Package Radiometrix Ltd M48A Modem Data Sheet page 7 Radiometrix Ltd Application circuit M48A Modem Data Sheet BiM, NIM & USX series radio transceiver + M48A modem interface for RS232 port page 8 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 copyrighted 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 believed 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 Ltd does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of third parties which may result from the use of its products. This data sheet neither states nor implies warranty of any kind, including fitness for any particular application. These radio devices may 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 particular equipment. Further details are available on The Office of Communications (Ofcom) web site: http://www.ofcom.org.uk/radiocomms/ifi/ Information Requests Ofcom Riverside House 2a Southwark Bridge Road London SE1 9HA Tel: +44 (0)845 456 3000 or 020 7981 3040 Fax: +44 (0)20 7783 4033 information.requests@ofcom.org.uk European Radiocommunications Office (ERO) Peblingehus Nansensgade 19 DK 1366 Copenhagen Tel. +45 33896300 Fax +45 33896330 ero@ero.dk www.ero.dk |
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