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rev. b information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. a cmos monolithic 256 3 18 color palette ram-dac adv476 one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 617/329-4700 fax: 617/326-8703 functional block diagram features personal system/2* and vga* compatible plug-in replacement for inmos 171/176 66 mhz pipelined operation three 6-bit d/a converters 256 3 18 color palette ram rs-343a/rs-170 compatible outputs blank on all three channels standard mpu interface asynchronous access to all internal registers 1 5 v cmos monolithic construction low power dissipation standard 28-pin, 0.6" dip and 44-pin plcc applications high resolution color graphics cae/cad/cam applications image processing instrumentation desktop publishing available clock rates 66 mhz 50 mhz 35 mhz general description the adv476 (adv ? ) is a pin compatible and software compat- ible ram-dac designed specifically for vga and personal system/2 color graphics. the adv476 is a complete analog output ram-dac on a single monolithic chip. the part contains a 256 3 18 color lookup table, a pixel mask register as well as a triple 6-bit video d/a converter. the adv476 is capable of simultaneously dis- playing up to 256 colors, from a total color palette of 262,144 addressable colors. the on-chip asynchronous mpu bus allows access to the color lookup table without affecting the input video data via the pixel port. the pixel read mask register provides a convenient way of altering the displayed colors without updating the color lookup table. the adv476 is capable of generating rgb video output signals which are compatible with rs-343a and rs-170 video standards, without requiring external buffering. the adv476 is fabricated in a +5 v cmos process. its mono- lithic cmos construction ensures greater functionality with low power dissipation and small board area. the part is packaged in a 0.6", 28-pin dip and a 44-pin plcc. product highlights 1. standard video refresh rates, 35 mhz, 50 mhz and 66 mhz. 2. fully compatible with vga and personal system/2 color graphics. 3. guaranteed monotonic. integral and differential linearity guaranteed to be a maximum of 1 lsb. 4. low glitch energy, 75 pv secs. * personal system/2 and vga are trademarks of international business machines corp. adv is a registered trademark of analog devices, inc.
rev. b C2C adv476Cspecifications (v cc = +5 v 6 10%, i ref = 8.88 ma. all specifications t min to t max 1 unless otherwise noted.) parameter all versions units test conditions/comments static performance resolution (each dac) 6 bits accuracy (each dac) integral nonlinearity 0.5 lsb max guaranteed monotonic full scale error 5 % max full scale = 2.15 3 i ref 3 r l , i ref = 8.39 ma blank level 0.5 lsb max blank = logic low offset error 0.5 lsb max blank = logic high digital inputs input high voltage, v inh 2 v min input low voltage, v inl 0.8 v max input current, i in 10 m a max v cc = 5.5 v, v in = 0.4 v to v cc input current ( rd input only) 100 m a max v cc = 5.5 v, v in = 0.4 v to v cc input capacitance, c in 7 pf typ digital outputs output high voltage, v oh 2.4 v min i source = 500 m a, v cc = 4.5 v output low voltage, v ol 0.4 v max i sink = 5.0 ma, v cc = 4.5 v floating-state leakage current 50 m a max v cc = 5.5 v, 0.4 v < v in < v cc floating-state output capacitance 7 pf typ analog outputs max output voltage 1.5 v min io < 10 ma, io = 2.15 3 i ref max output current 21 ma min vo 1 v dac to dac matching 2 2.5 % max analog output capacitance 10 pf typ blank = logic low current reference input current (i ref ) range C3/C10 ma min/ma max voltage at i ref v cc C3/v cc v min/v max i ref = 8.88 ma power supply supply voltage, v cc 4.5/5.5 v min/v max supply current, i cc 220 ma max f max = 66 mhz io = 2.15 3 i ref , d0Cd7 unloaded power supply rejection ratio 6 %/v 4.5 < v cc < 5.5 v, io = 2.15 3 i ref , r l = 37.5 w , c l = 30 pf, i ref = 8.88 ma. dynamic performance clock and data feedthrough 3, 4 C35 db typ glitch impulse 3, 4 75 pv secs typ notes 1 temperature range (t min to t max ); 0 to +70 c. 2 relative to the midpoint of the distribution of the three dacs measured at full scale. 3 ttl input values are 0 to 3 volts, with input rise/fall times 3 ns, measured between the 10% and 90% points. timing reference points at 50% for inputs and out- puts. analog output load 10 pf, 37.5 w . d0Cd7 output load 50 pf. see timing notes in figure 2. 4 clock and data feedthrough is a function of the amount of overshoot and undershoot on the digital inputs. for this test, the digital inputs have a 1 k w resistor to ground and are driven by 74hc logic. glitch impulse includes clock and data feedthrough, C3 db test bandwidth = 2 3 clock rate. specifications subject to change without notice.
adv476 rev. b C3C timing characteristics 1 parameter 66 mhz version 50 mhz version 35 mhz version units conditions/comments f max 66 50 35 mhz clock rate t 1 10 10 15 ns min rs0, rs1 setup time t 2 10 10 15 ns min rs0, rs1 hold time t 3 5 5 5 ns min rd asserted to data bus driven t 4 40 40 40 ns max rd asserted to data valid t 5 20 20 20 ns max rd negated to data bus 3-stated t 6 10 10 15 ns min write data setup time t 7 10 10 15 ns min write data hold time t 8 50 50 50 ns min rd , wr pulse width low t 9 4 3 t 12 4 3 t 12 4 3 t 12 ns min rd , wr pulse width high t 10 3 3 4 ns min pixel & control setup time t 11 3 3 4 ns min pixel & control hold time t 12 15.3 20 28 ns min clock cycle time t 13 5 6 7 ns min clock pulse width high time t 14 5 6 9 ns min clock pulse width low time t 15 30 30 30 ns max analog output delay 5 5 5 ns min t 16 6 8 8 ns max analog output rise/fall time t 17 3 15.3 20 25 ns typ analog output settling time t 18 2 2 2 ns min analog output skew t pd 4 4 4 clocks pipeline delay notes 1 ttl input values are 0 to 3 volts, with input rise/fall times 3 ns, measured between the 10% and 90% points. timing reference points at 50% for inputs and outputs. analog output load 10 pf, 37.5 w . d0Cd7 output load 50 pf. see timing notes in figure 2. 2 temperature range (t min to t max ); 0 to +70 c 3 settling time does not include clock and data feedthrough. for this test, the digital inputs have a 1 k w resistor to ground and are driven by 74hc logic. specifications subject to change without notice. figure 1. mpu read/write timing figure 2. video input/output timing (v cc = +5 v 6 10%. all specifications t min to t max 2 )
adv476 rev. b C4C absolute maximum ratings 1 v cc to gnd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 v voltage on any digital pin . . . . . gnd C 0.5 v to v cc + 0.5 v ambient operating temperature (t a ) . . . . . C55 c to +125 c storage temperature (t s ) . . . . . . . . . . . . . . C65 c to +150 c junction temperature (t j ) . . . . . . . . . . . . . . . . . . . . +150 c lead temperature (soldering, 10 secs) . . . . . . . . . . . +300 c vapor phase soldering (1 minute) . . . . . . . . . . . . . . . +220 c red, green, blue to gnd 2 . . . . . . . . . . . . . . . . . . 0 v to v cc notes 1 stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only and functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2 analog output short circuit to any power supply or common can be of an indefinite duration. ordering guide 1, 2 package model speed package type option 3 ADV476KN35 35 mhz 28-pin dip n-28 adv476kn50 50 mhz 28-pin dip n-28 adv476kn66 66 mhz 28-pin dip n-28 adv476kp35 35 mhz 44-pin plcc p-44a adv476kp50 50 mhz 44-pin plcc p-44a adv476kp66 66 mhz 44-pin plcc p-44a notes 1 all devices are specified for 0 c to +70 c operation. 2 devices are packaged in 0.6" 28-pin plastic dips (n-28), and 44-pin j-leaded plcc (p-44a). 3 n = plastic dip; p = plastic leaded chip carrier. recommended operating conditions parameter symbol min typ max units power supply v cc 4.5 5.00 5.5 volts ambient operating temperature t a 0 +70 c output load r l 37.5 w reference current i ref C3 C10 ma warning! esd sensitive device caution esd (electrostatic discharge) sensitive device. electrostatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge without detection. although the adv476 features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality. pin configurations plcc dip the above pins allow the adv476kp (44-pin plcc) to be al- ternatively driven by a voltage reference. if it is desired to use a voltage reference configuration instead of the current reference configuration described in this data sheet, the above listed pins must be connected as described in figure 6 of the adv478/ adv471 data sheet of this reference manual.
adv476 rev. b C5C pin function description pin mnemonic function blank composite blank control input (ttl compatible). a logic zero on this control input drives the analog outputs to the blanking level, as shown in table v. the blank signal is latched on the rising edge of pclk. while blank is a logical zero, the pixel inputs are ignored. pclk clock input (ttl compatible). the rising edge of pclk latches the p0Cp7 data inputs and the blank control input. it is typically the pixel clock rate of the video system. pclk should be driven by a dedicated ttl buffer. p0Cp7 pixel select inputs (ttl compatible). these inputs specify, on a pixel basis, which one of the 256 entries in the color palette ram is to be used to provide color information. p0Cp7 pixel select inputs are latched on the rising edge of pclk. p0 is the lsb. unused pixel select inputs should be connected to gnd. red, green, red, green and blue current outputs. these high impedance current sources are capable of directly driving a blue doubly terminated 75 w coaxial cable, as shown in figure 4a. all three current outputs should have similar out- put loads whether or not they are all being used. v cc analog power supply (5 v 10%). gnd analog ground. i ref current reference input. the relationship between the current input and the full scale output voltage of the dacs is given by the following expression: i ref = vo (full scale)/2.15 3 r l r l = load resistance wr write control input (ttl compatible). wr must be at logical zero when writing data to the device. d0Cd7 data is latched on the rising edge of wr . see figure 1. rd read control input (ttl compatible). rd must both be at logical zero when reading data from the device. see figure 1. rs0, rs1 command control inputs (ttl compatible). rs0 and rs1 specify the type of read or write operation being car- ried out, i.e., address register or color palette ram read or write operations. see tables i, ii, iii. d0Cd7 data bus (ttl compatible). data is transferred to and from the address register and the color palette ram over this 8-bit bidirectional data bus. d0 is the least significant bit. terminology blanking level the level separating the sync portion from the video portion of the waveform. usually referred to as the front porch or back porch. at 0 ire units, it is the level which will shut off the pic- ture tube, resulting in the blackest possible picture. color video (rgb) this usually refers to the technique of combining the three pri- mary colors of red, green and blue to produce color pictures within the usual spectrum. in rgb monitors, three dacs are required, one for each color. gray scale the discrete levels of video signal between reference black and reference white levels. an 8-bit dac contains 256 different levels while a 6-bit dac contains 64. raster scan the most basic method of sweeping a crt one line at a time to generate and display images. reference black level the maximum negative polarity amplitude of the video signal. reference white level the maximum positive polarity amplitude of the video signal. video signal that portion of the composite video signal which varies in gray scale levels between reference white and reference black. also referred to as the picture signal, this is the portion which may be visually observed.
adv476 rev. b C6C mpu interface as illustrated in the functional block diagram, the adv476 sup- ports a standard mpu bus interface, allowing the mpu direct access to the color palette ram. the rs0 and rs1 control inputs specify whether the mpu is accessing the address register or the color palette ram, as shown in table i. the 8-bit address register is used to address the color palette ram, eliminating the requirement for external address multiplexers. table i. control input truth table rs1 rs0 addressed by mpu 0 0 pixel address register (ram write mode) 1 1 pixel address register (ram read mode) 0 1 color palette ram 1 0 pixel read mask register to write color data, the mpu writes to the address register with the 8-bit address of the color palette ram location which is to be modified. the mpu performs three successive write cycles (six bits of red data, six bits of green data and six bits of blue data). during the blue write cycle, the three bytes of color infor- mation are concatenated into an 18-bit word and written to the location specified by the address register. the address register then automatically increments to the next location which the mpu may modify by simply writing another sequence of red, green and blue data. to read back color data, the mpu loads the address register with the address of the color palette ram location to be read. the mpu performs three successive read cycles (6 bits each of red, green and blue data). following the blue read cycle, the address register increments to the next location which the mpu may read by simply reading another sequence of red, green and blue data. this 6-bit color data is right justified, i.e., the lower six bits of the data bus with d0 being the lsb and d5 the msb. d6 and d7 are ignored during a color write cycle and are set to zero during a color read cycle. during color palette ram access, the address register resets to 00h following a blue read or write operation to ram location ffh. the mpu interface operates asynchronously to the pixel clock. data transfers between the color palette ram and the color registers (r, g, and b in the block diagram) are synchronized by internal logic, and occur in the period between mpu accesses. color (rgb) data is normally loaded to the color palette ram during video screen retrace, i.e., during the video waveform blanking period, see figure 5. to keep track of the red, green and blue read/write cycles, the address register has two additional bits (addra, addrb) that count modulo three, as shown in table ii. they are reset to zero when the mpu writes to the address register, and are not reset to zero when the mpu reads the address register. the mpu does not have access to these bits. the other eight bits of the address register, incremented following a blue read or write cycle, (addr0C7) are accessible to the mpu, and are used to address color palette ram locations, as shown in table iii. addr0 is the lsb when the mpu is accessing the ram. the mpu may read the address register at any time without modify- ing its contents or the existing read/write mode. figure 1 illustrates the mpu read/write timing and table iii shows the associated functional instructions. table ii. address register (addr) operation value rs1 rs0 addressed by mpu addra,b (counts modulo 3) 00 red value 01 green value 10 blue value addr0C7 (counts binary) 00hCffh 0 1 color palette ram table iii. truth table for read/write operations rd wr rs0 rs1 addra addrb operation performed 1000x x write address register; d0Cd7 ? addr0C7 0 ? addra,b 10100 0 write red value; increment addraCb 10100 1 write green value; increment addraCb 10101 0 write blue value; modify ram location increment addr0C7 increment addraCb 0111x x read address register; addr0C7 ? d0Cd7 01100 0 read red value; increment addraCb 01100 1 read green value; increment addraCb 01101 0 read blue value; increment addr0C7 increment addraCb 0 0 x x x x invalid operation
adv476 rev. b C7C frame buffer interface the p0-p7 inputs are used to address the color palette ram, as shown in table iv. these inputs are latched on the rising edge of pclk and address any of the 256 locations in the color pal- ette ram. the addressed location contains 18 bits of color (6 bits of red, 6 bits of green and 6 bits of blue) information. this data is transferred to the three dacs and is then converted to an analog output (red, green, blue), these outputs then control the red, green and blue electron guns in the monitor. the blank input is also latched on the rising edge of pclk. this is to maintain synchronization with the color data. table iv. pixel select/color palette control truth table p0Cp7 addressed by frame buffer 00h color palette ram location 00h 01h color palette ram location 01h ??? ??? ffh color palette ram location ffh pixel read mask register the pixel read mask register in the adv476 can be used to implement register level pixel processing, thereby cutting down on software overhead. this is achieved by gating the input pixel stream (p0Cp7) with the contents of the pixel read mask regis- ter. the operation is a bitwise logical anding of the pixel data. the contents of this register can be accessed and altered at any time by the mpu (d0Cd7). table i shows the relevant control signals. this pixel masking operation can be used to alter the displayed colors without changing the contents of either the video frame buffer or the color palette ram. the effect of this operation is to partition the color palette into a user determined number of color planes. this process can be used for special effects includ- ing animation, overlays and flashing objects. (see also application note entitled animation using the pixel read mask register of the adv47x series of video ram- dacs, available from analog devices (pub no. e1316C15C10/89). figure 3. block diagram showing pixel read mask register analog interface the adv476 has three analog outputs, corresponding to the red, green and blue video signals. the red, green and blue analog outputs of the adv476 are high impedance current sources. each one of these three rgb current outputs is capable of directly driving a 37.5 w load, such as a doubly-terminated 75 w coaxial cable. figure 4a shows the required configuration for each of the three rgb outputs con- nected into a doubly-terminated 75 w load. this arrangement will develop rs-343a video output voltage levels across a 75 w monitor. a simple method of driving rs-170 video levels into a 75 w monitor is shown in figure 4b. the output current levels of the dacs remain unchanged but the source termination figure 4a. recommended analog output termination for rs-343a resistance, z s on each of the three dacs is increased from 75 w to 150 w . more detailed information regarding load terminations for vari- ous output configurations, including rs-343a and rs-170, is available in an application note entitled video formats & required load terminations, available from analog devices. figure 5 shows the video waveforms associated with the three rgb outputs, driving the doubly terminated 75 w load of fig- ure 4a. the blank control input drives the analog outputs to the black level. blank is asserted prior to horizontal and ver- tical screen retrace. table v details how the blank input modifies the output levels. figure 4b. recommended analog output termination for rs-170
adv476 rev. b C8C figure 5. rgb video output waveform table v. video output truth table red, green, dac description blue, (ma) 1 blank input data white level 19.05 1 ffh video video 1 data black level 0 1 00h blank level 0 0 xxh note 1 typical with full scale red, green, blue = 19.05 ma. i ref = 8.88 ma. reference input the adv476 requires an active current reference to enable the dacs provide stable and accurate video output levels. the rela- tionship between the output voltage and the required input ref- erence current is given by: i ref = vo ( full scale ) 2.15 r l where r l = 37.5 w (for doubly terminated 75 w load) = 75 w (for singly terminated 75 w load) and vo = 0.714 v (rs-343a video levels) = 1.0 v (rs-170 video levels). in a standard application which requires rs-343a video levels to be driven into a doubly terminated 75 w load (r l = 37.5 w ), the necessary reference input current is: i ref = 8.88 ma . to drive the same levels into a singly terminated 75 w load (r l = 75 w ), the reference current is: i ref = 4.44 ma . a suggested current reference design for the doubly terminated case, with rs-343a video levels and based on the lm334, a three-terminal adjustable current source, is shown in figure 6. figure 6. current reference design using an lm334 current source
adv476 rev. b C9C pc board layout considerations the adv476 is optimally designed for lowest noise perfor- mance, both radiated and conducted noise. for optimum sys- tem noise performance, it is imperative that great care be given to the pc board layout. the layout should be optimized for low- est noise on the adv476 power and ground lines. this can be achieved by shielding the digital inputs and providing good decoupling. the lead length between groups of v cc and gnd pins should by minimized so as to minimize inductive ringing. ground planes the ground plane should encompass all adv476 ground pins, voltage reference circuitry, power supply bypass circuitry, the analog output traces and all the digital signal traces leading up to the adv476. power planes the pc board layout should have two distinct power planes, one for analog circuitry and one for digital circuitry. the analog power plane (v cc ) should encompass the adv476 and all asso- ciated analog circuitry. this power plane should be connected to the regular pcb power plane at a single point through a fer- rite bead, as illustrated in figure 7. this bead should be located within three inches of the adv476. the pcb power plane should provide power to all digital logic on the pc board, and the analog power plane should provide power to all adv476 power pins, current reference circuitry and any output amplifiers. the pcb power and ground planes should not overlay portions of the analog power plane. keeping the pcb power and ground planes from overlaying the analog power plane will contribute to a reduction in plane-to-plane noise coupling. supply decoupling noise on the analog power plane can be further reduced by the use of multiple decoupling capacitors, see figure 7. optimum performance is achieved by the use of 0.1 m f ceramic capacitors. this should be done by placing the capacitors as close as possible to the device with the capacitor leads as short as possible, thus minimizing lead inductance. it is important to note that while the adv476 contains circuitry to reject power supply noise, this rejection decreases with fre- quency. if a high frequency switching power supply is used, the designer should pay close attention to reducing power supply noise. a dc power supply filter (murata bnx002) will provide emi suppression between the switching power supply and the main pcb. alternatively, consideration could be given to using a three terminal voltage regulator. digital signal interconnect the digital signal lines to the adv476 should be isolated as much as possible from the analog outputs and other analog circuitry. digital signal lines should not overlay the analog power plane. due to the high clock rates used, long clock lines to the adv476 should be avoided so as to minimize noise pickup. any active pull-up termination resistors for the digital inputs should be connected to the regular pcb power plane and not the analog power plane. analog signal interconnect the adv476 should be located as close as possible to the out- put connectors thus minimizing noise pickup and reflections due to impedance mismatch. the video output signals should overlay the ground plane, and not the analog power plane, thereby maximizing the high fre- quency power supply rejection. for optimum performance, the analog outputs should each have a source termination resistance to ground of 75 w . this termi- nation resistance should be as close as possible to the adv476 to minimize reflections. note: for additional information on pc board-layout see application note design and layout of a video graphics system for reduced emi, available from analog devices (pub. no. e1309C15C10/89).
adv476 rev. b C10C figure 7. adv476 typical connection diagram and component list outline dimensions dimensions shown in inches and (mm). 28-pin plastic dip (n-28) figure 8. connection of v ref and comp with the adv476kp (44-pin plcc)
C11C
adv476 rev. b C12C c1267C10C3/89 printed in u.s.a.

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