HI-8581PQI

HI-8581 June 2001 GENERAL DESCRIPTION The HI-8581 device from Holt Integrated Circuits is a silicon gate CMOS device for interfacing a 16-bit parallel data bus directly to the ARINC 429 serial bus. The device provides two receivers, an independent transmitter and line driver capability in a single package. The receiver input circuitry and logic are designed to meet the ARINC 429 specifications for loading, level detection, timing, and protocol. The transmitter section provides the ARINC 429 communication protocol and the line driver circuits provide the ARINC 429 output levels. The 16-bit parallel data bus exchanges the 32-bit ARINC data word in two steps when either loading the transmitter or interrogating the receivers. The data bus interfaces with CMOS and TTL. Timing of all the circuitry begins with the master clock input, CLK. For ARINC 429 applications, the master clock frequency is 1 MHz. Each independent receiver monitors the data stream with a sampling rate 10 times the data rate. The sampling rate is software selectable at either 1MHz or 125KHz. The results of a parity check are available as the 32nd ARINC bit. The HI-8581 examines the null and data timings and will reject erroneous patterns. For example, with a 125 KHz clock selection, the data frequency must be between 10.4 KHz and 15.6 KHz. The transmitter has a First In, First Out (FIFO) memory to store 8 ARINC words for transmission. The data rate of the transmitter is software selectable by dividing the master clock, CLK, by either 10 or 80. The master clock is used to set the timing of the ARINC transmission within the required resolution. FEATURES ! ARINC specification 429 compatible ! Direct receiver and transmitter interface to ARINC bus in a single device. ! 16-Bit parallel data bus. ! Timing control 10 times the data rate ! Selectable data clocks ! Receiver error rejection per ARINC specification 429 ! Automatic transmitter data timing ! Self test mode ! Parity functions ! Low power ! Industrial & full military temperature ranges PIN CONFIGURATION (Top View) 429DI2(B) - 1 D/R1 - 2 D/R2 - 3 SEL - 4 EN1 - 5 EN2 - 6 BD15 - 7 BD14 - 8 BD13 - 9 BD12 - 10 BD11 - 11 HI-8581PQI & HI-8581PQT 33 - ENTX 32 - N/C 31 - V+ 30 - TXB(OUT) 29 - TXA(OUT) 28 - V27 - GND 26 - TX/R 25 - PL2 24 - PL1 23 - BD00 APPLICATIONS ! Avionics data communication ! Serial to parallel conversion ! Parallel to serial conversion (See page 13 for additional pin configurations) (DS8581 Rev. A) HOLT INTEGRATED CIRCUITS 1 06/01 HI-8581 SIGNAL VCC V+ V429DI1 (A) 429DI1 (B) 429DI2 (A) 429DI2 (B) D/R1 D/R2 SEL EN1 EN2 BD15 BD14 BD13 BD12 BD11 BD10 BD09 BD08 BD07 BD06 GND BD05 BD04 BD03 BD02 BD01 BD00 TX/R PL1 PL2 TXA(OUT) TXB(OUT) ENTX CWSTR CLK TX CLK MR FUNCTION POWER POWER POWER INPUT INPUT INPUT INPUT OUTPUT OUTPUT INPUT INPUT INPUT I/O I/O I/O I/O I/O I/O I/O I/O I/O I/O POWER I/O I/O I/O I/O I/O I/O OUTPUT INPUT INPUT OUTPUT OUTPUT INPUT INPUT INPUT OUTPUT INPUT +5V ±5% +9.5V to +12.6V -9.5V to -12.6V DESCRIPTION ARINC receiver 1 positive input ARINC receiver 1 negative input ARINC receiver 2 positive input ARINC receiver 2 negative input Receiver 1 data ready flag Receiver 2 data ready flag Receiver data byte selection (0 = BYTE 1) (1 = BYTE 2) Data Bus control, enables receiver 1 data to outputs Data Bus control, enables receiver 2 data to outputs if EN1 is high Data Bus Data Bus Data Bus Data Bus Data Bus Data Bus Data Bus Data Bus Data Bus Data Bus 0V Data Bus Data Bus Data Bus Data Bus Data Bus Data Bus Transmitter ready flag. Goes low when ARINC word loaded into FIFO. Goes high After transmission and FIFO empty. Latch enable for byte 1 entered from data bus to transmitter FIFO. Latch enable for byte 2 entered from data bus to transmitter FIFO. Must follow PL1. Line driver output - A side Line driver output - B side Enable Transmission Clock for control word register Master Clock input Transmitter Clock equal to Master Clock (CLK), divided by either 10 or 80. Master Reset, active low HOLT INTEGRATED CIRCUITS 2 HI-8581 FUNCTIONAL DESCRIPTION CONTROL WORD REGISTER The HI-8581 contains 10 data flip flops whose D inputs are connected to the data bus and clocks connected to CWSTR. Each flip flop provides options to the user as follows: DATA BUS ARINC 429 DATA FORMAT The following table shows the bit positions in exchanging data with the receiver or the transmitter. ARINC bit 1 is the first bit transmitted or received. BYTE 1 BD BD BD BD BD BD BD BD BD BD BD BD BD BD BD BD 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 13 12 11 10 9 31 30 32 1 2 3 4 5 6 7 8 DATA BUS PIN BDO5 FUNCTION CONTROL DESCRIPTION If enabled, an internal connection is made passing 429DO and 429DO to the receiver logic inputs If enabled, ARINC bits 9 and, 10 must match the next two control word bits If Receiver 1 Decoder is enabled, the ARINC bit 9 must match this bit If Receiver 1 Decoder is enabled, the ARINC bit 10 must match this bit If enabled, ARINC bits 9 and 10 must match the next two control word bits If Receiver 2 Decoder is enabled, then ARINC bit 9 must match this bit If Receiver 2 Decoder is enabled, then ARINC bit 10 must match this bit Logic 0 enables normal odd parity and Logic 1 enables even parity output in transmitter 32nd bit CLK is divided either by 10 or 80 to obtain XMTR data clock CLK is divided either by 10 or 80 to obtain RCVR data clock ARINC BIT SELF TEST 0 = ENABLE BYTE 2 DATA BUS ARINC BIT BD BD BD BD BD BD BD BD BD BD BD BD BD BD BD BD 15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 BDO6 RECEIVER 1 DECODER 1 = ENABLE BDO7 - - THE RECEIVERS ARINC BUS INTERFACE Figure 1 shows the input circuit for each receiver. The ARINC 429 specification requires the following detection levels: BDO8 - - BDO9 RECEIVER 2 DECODER 1 = ENABLE BD10 - - STATE ONE NULL ZERO DIFFERENTIAL VOLTAGE +6.5 Volts to +13 Volts +2.5 Volts to -2.5 Volts -6.5 Volts to -13 Volts BD11 - - BD12 INVERT XMTR PARITY XMTR DATA CLK SELECT RCVR DTA CLK SELECT 1 = ENABLE The HI-8581 guarantees recognition of these levels with a common mode Voltage with respect to GND less than ±5V for the worst case condition (4.75V supply and 13V signal level). The tolerances in the design guarantee detection of the above levels, so the actual acceptance ranges are slightly larger. If the ARINC signal is out of the actual acceptance ranges, including the nulls, the chip rejects the data. BD13 0 = ÷10 1 = ÷80 0 = ÷10 1 = ÷80 BD14 HOLT INTEGRATED CIRCUITS 3 HI-8581 FUNCTIONAL DESCRIPTION (con't) RECEIVER LOGIC OPERATION Figure 2 shows a block diagram of the logic section of each receiver. BIT TIMING The ARINC 429 specification contains the following timing specification for the received data: HIGH SPEED LOW SPEED 100K BPS ± 1% 12K -14.5K BPS 1.5 ± 0.5 µsec 10 ± 5 µsec 1.5 ± 0.5 µsec 10 ± 5 µsec 5 µsec ± 5% 34.5 to 41.7 µsec 3. Each data bit must follow its predecessor by not less than 8 samples and no more than 12 samples. In this manner the bit rate is checked. With exactly 1MHz input clock frequency, the acceptable data bit rates are as follows: HIGH SPEED DATA BIT RATE MIN DATA BIT RATE MAX 83K BPS 125K BPS LOW SPEED 10.4K BPS 15.6K BPS BIT RATE PULSE RISE TIME PULSE FALL TIME PULSEWIDTH 4. TheWordGaptimersamplestheNullshiftregister every 10 input clocks (80 for low speed) after the last data bit of a Valid reception. If the Null is present, theWordGapcounter Is incremented. A count of 3 will enable the next reception. RECEIVER PARITY The receiver parity circuit counts Ones received, including the parity bit, ARINC bit 32. If the result is odd, then "0" will appear in the 32nd bit. Again the HI-8581 accepts signals that meet these specifications and rejects outside the tolerances. The way the logic operation achieves this is described below: 1. Key to the performance of the timing checking logic is an accurate 1MHz clock source. Less than 0.1% error is recommended. 2. The sampling shift registers are 10 bits long and must show three consecutive Ones, Zeros or Nulls to be considered valid data. Additionally, for data bits, the One or Zero in the upper bits of the sampling shift registers must be followed by a Null in the lower bits within the data bit time. For a Null in the word gap, three consecutive Nulls must be found in both the upper and lower bits of the sampling shift register. In this manner the minimum pulse width is guaranteed. RETRIEVING DATA Once 32 valid bits are recognized, the receiver logic generates an End of Sequence (EOS). If the receiver decoder is enabled and the 9th and 10th ARINC bits match the control word program bits or if the receiver decoder is disabled, then EOS clocks the data ready flag flip flop to a "1", D/R1 or D/R2 (or both) will go low. The data flag for a receiver will remain low until after both ARINC bytes from that receiver are retrieved. This is accomplished by first activating EN with SEL, the byte selector, low to retrieve the first byte and then activating EN with SEL high to retrieve the second byte. ENI retrieves data from receiver 1 and EN2 retrieves data from receiver 2. If another ARINC word is received, and a new EOS occurs before the two bytes are retrieved, the data is overwritten by the new word. TO PINS SEL EN D/R DECODER CONTROL BITS MUX CONTROL 32 TO 16 DRIVER CONTROL BIT BD14 CLOCK OPTION CLOCK CLK / LATCH ENABLE CONTROL BITS 9 & 10 32 BIT LATCH BIT COUNTER AND END OF SEQUENCE 32 BIT SHIFT REGISTER DATA PARITY CHECK 32ND BIT BIT CLOCK EOS EOS ONES SHIFT REGISTER WORD GAP WORD GAP TIMER BIT CLOCK START END NULL SHIFT REGISTER SEQUENCE CONTROL ZEROS SHIFT REGISTER ERROR DETECTION ERROR CLOCK FIGURE 2. RECEIVER BLOCK DIAGRAM HOLT INTEGRATED CIRCUITS 4 HI-8581 TRANSMITTER A block diagram of the transmitter section is shown in Figure 3. TRANSMITTER PARITY The parity generator counts the ONES in the 31-bit word. If the BD12 control word bit is set low, the 32nd bit transmitted will make parity odd. If the control bit is high, the parity is even. FIFO OPERATION The FIFO is loaded sequentially by first pulsing PL1 to load byte 1 and then PL2 to load byte 2. The control logic automatically loads the 31 bit word in the next available position of the FIFO. If TX/R, the transmitter ready flag is high (FIFO empty), then 8 words, each 31 bits long, may be loaded. If TX/R is low, then only the available positions may be loaded. If all 8 positions are full, the FIFO ignores further attempts to load data. SELF TEST If the BD05 control word bit is set low, 429DO or 429DO become inputs to the receiver bypassing the interface circuitry. SYSTEM OPERATION The two receivers are independent of the transmitter. Therefore, control of data exchanges is strictly at the option of the user. The only restrictions are: 1. The received data may be overwritten if not retrieved within one ARINC word cycle. 2. The FIFO can store 8 words maximum and ignores attempts to load addition data if full. 3. Byte 1 of the transmitter data must be loaded first. 4. Either byte of the received data may be retrieved first. Both bytes must be retrieved to clear the data ready flag. 5. After ENTX, transmission enable, goes high it cannot go low until TX/R, transmitter ready flag, goes high. Otherwise, one ARINC word is lost during transmission. DATA TRANSMISSION When ENTX goes high, enabling transmission, the FIFO positions are incremented with the top register loading into the data transmission shift register. Within 2.5 data clocks the first data bit appears at either 429DO or 429DO. The 31 bits in the data transmission shift register are presented sequentially to the outputs in the ARINC 429 format with the following timing: HIGH SPEED 10 Clocks 5 Clocks 5 Clocks 40 Clocks LOW SPEED 80 Clocks 40 Clocks 40 Clocks 320 Clocks ARINC DATA BIT TIME DATA BIT TIME NULL BIT TIME WORD GAP TIME The word counter detects when all loaded positions are transmitted and sets the transmitter ready flag, TX/R, high. HOLT INTEGRATED CIRCUITS 5 HI-8581 LINE DRIVER OPERATION The line driver in the HI-8581 is designed to directly drive the ARINC 429 bus. The two ARINC outputs (TXA(OUT) and TXB(OUT)) provide a differential voltage to produce a +10 volt One, a -10 volt Zero, and a 0 volt Null. Setting Control Register bit 13 to zero causes a slope of 1.5 µs on the ARINC outputs; a one in Control Register bit 13 causes a slope of 10 µs. Timing is set by on-chip resistor and capacitor and tested to be within ARINC requirements. No additional hardware is required to control the slope. The HI-8581 has 37.5 ohms in series with each line driver output. REPEATER OPERATION Repeater mode of operation allows a data word that has been received by the HI-8581 to be placed directly into its FIFO for transmission. Repeater operation is similar to normal receiver operation. In normal operation, either byte of a received data word may be read from the receiver latches first by use of SEL input. During repeater operation however, the lower byte of the data word must be read first. This is necessary because, as the data is being read, it is also being loaded into the FIFO and the transmitter FIFO is always loaded with the lower byte of the data word first. Signal flow for repeater operation is shown in the Timing Diagrams section. TXA(OUT) ARINC BIT TXB(OUT) DATA NULL DATA NULL DATA NULL BIT 30 BIT 31 BIT 32 WORD GAP BIT 1 NEXT WORD DATA BUS VALID tCWSET t CWHLD CWSTR t CWSTR t D/R t END/R t EN t SELEN tENSEL tENEN tDATAEN t ENDATA tSELEN tENSEL tD/REN DATA BUS t DATAEN tENDATA HOLT INTEGRATED CIRCUITS 6 HI-8581 DATA BUS BYTE 1 VALID BYTE 2 VALID tDWSET PL1 tDWHLD tDWSET tDWHLD tPL12 t PL PL2 tPL12 TX/R t PL tTX/R PL2 tDTX/R tPL2EN TX/R ENTX t ENTX/R ARINC BIT DATA BIT 1 ARINC BIT DATA BIT 2 t ENDAT ARINC BIT DATA BIT 32 +5V TXA(OUT) -5V +5V TXB(OUT) -5V +5V -5V tfx +10V V DIFF (TXA(OUT) - TXB(OUT)) 90% 10% +10V tfx 10% zero level 90% trx null level trx one level -10V HOLT INTEGRATED CIRCUITS 7 HI-8581 429DI BIT 32 t END/R D/R tD/R EN tD/REN t EN t ENEN t EN t SELEN SEL DON'T CARE tENSEL DON'T CARE tENPL PL1 tPLEN tENPL tSELEN t ENSEL t PLEN PL2 tTX/R TX/R tTX/REN ENTX tENTX/R tENDAT TXA(OUT) TXB(OUT) BIT 1 t DTX/R BIT 32 t NULL HOLT INTEGRATED CIRCUITS 8 HI-8581 Supply Voltages Vcc V+ VVoltage at pins ARINC inputs Voltage at any other pin -0.3V to +7V Power Dissipation at 25C Plastic PLCC/PQFP +13.0V Ceramic J-LEAD CERQUAD -13.0V -29V to +29V DC Current Drain per pin -0.3V to Vcc +0.3V Storage Temperature Range: Operating Temperature Range: (Industrial) (Military) 1.5 W, derate 10mW/°C 1.0 W, derate 7mW/°C ±10mA -65°C to +150°C -40°C to +85°C -55°C to +125°C NOTE: Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only. Functional operation of the device at these or any other conditions above those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Vcc = 5V ±5%, V+ = 10V , V- = -10V, GND = 0V, TA = Operating Temperature Range (unless otherwise specified). PARAMETER ARINC INPUTS Differential Input Voltage: ONE ZERO NULL Differential To GND To Vcc Input Sink Input Source Differential To GND To Vcc SYMBOL CONDITIONS LIMITS MIN TYP MAX UNIT VIH VIL VNUL RI RG RH IIH IIL CI CG CH Pins 4 to 5, 6 to 7: Common mode voltage less than ±4V with respect to GND 6.5 -13.0 -2.5 12 12 12 -450 10.0 -10.0 0 27 27 13.0 -6.5 2.5 V V V K K K Input Resistance: Input Current: Input Capacitance: (Guaranteed but not tested) BI-DIRECTIONAL INPUTS Input Voltage: Input Current: OTHER INPUTS Input Voltage: Input Current: 200 Pins 4 to 5, 6 to 7 20 20 20 µA µA pF pF pF Input Voltage HI Input Voltage LO Input Sink Input Source VIH VIL IIH IIL 2.1 0.7 1.5 -1.5 V V µA µA Input Voltage HI Input Voltage LO Input Sink Input Source VIH VIL IIH IIL 3.5 0.7 10 -20 V V µA HOLT INTEGRATED CIRCUITS 9 HI-8581 Vcc = 5V ±5%, V+ = 10V, V- = -10V, GND = 0V, TA = Operating Temperature Range (unless otherwise specified). PARAMETER ARINC OUTPUTS ARINC output voltage One or zero Null ARINC output current OTHER OUTPUTS Output Voltage: Output Current: (Bi-directional Pins) Output Current: (All Other Outputs) Output Capacitance: Operating Voltage Range Logic "1" Output Voltage Logic "0" Output Voltage Output Sink Output Source Output Sink Output Source SYMBOL CONDITIONS LIMITS MIN TYP MAX UNIT VDOUT VNOUT IOUT no load and magnitude at pin " " " " " " 4.50 -0.25 80 5.00 5.50 0.25 V V mA VOH VOL IOL IOH IOL IOH CO IOH = -1.5mA IOL = 2.6mA VOUT = 0.4V VOUT = VCC - 0.4V VOUT = 0.4V VOUT = VCC - 0.4V 2.7 0.4 3.0 1.1 2.6 1.1 15 V V mA mA mA mA pF VCC V+ VOperating Supply Current VCC V+ VICC1 IDD1 IEE1 4.75 9.5 -9.5 5.25 12.6 -12.6 V V V 20 16 16 mA mA mA HOLT INTEGRATED CIRCUITS 10 HI-8581 Vcc = 5V, V+=10V, V- = -10V, GND = 0V, TA = Oper. Temp. Range and fclk = 1MHz +0.1% with 60/40 duty cycle PARAMETER CONTROL WORD TIMING Pulse Width - CWSTR Setup - DATA BUS Valid to CWSTR HIGH Hold - CWSTR HIGH to DATA BUS Hi-Z RECEIVER TIMING Delay - Start ARINC 32nd Bit to D/R LOW: High Speed Low Speed Delay - D/R LOW to EN L0W Delay - EN LOW to D/R HIGH Setup - SEL to EN L0W Hold - SEL to EN HIGH Delay - EN L0W to DATA BUS Valid Delay - EN HIGH to DATA BUS Hi-Z Pulse Width - EN1 or EN2 Spacing - EN HIGH to next EN L0W FIFO TIMING Pulse Width - PL1 or PL2 Setup - DATA BUS Valid to PL HIGH Hold - PL HIGH to DATA BUS Hi-Z Spacing - PL1 or PL2 Delay - PL2 HIGH to TX/R LOW TRANSMISSION TIMING Spacing - PL2 HIGH to ENTX HIGH Delay - 32nd ARINC Bit to TX/R HIGH Spacing - TX/R HIGH to ENTX L0W LINE DRIVER OUTPUT TIMING Delay - ENTX HIGH to TXA(OUT) or TXB(OUT): High Speed Delay - ENTX HIGH to TXA(OUT) or TXB(OUT): Low Speed Line driver transition differential times: (High Speed) high to low low to high high to low low to high SYMBOL LIMITS MIN TYP MAX UNITS tCWSTR tCWSET tCWHLD 50 50 0 ns ns ns tD/R tD/R tD/REN tEND/R tSELEN tENSEL tENDATA tDATAEN tEN tENEN 80 50 0 16 128 200 0 0 50 50 80 30 µs µs ns ns ns ns ns ns ns ns tPL tDWSET tDWHLD tPL12 tTX/R 50 50 0 0 840 ns ns ns ns ns tPL2EN tDTX/R tENTX/R 0 50 0 µs ns ns tENDAT tENDAT tfx trx tfx trx 1.0 1.0 5.0 5.0 1.5 1.5 10 10 25 200 2.0 2.0 15 15 µs µs µs µs µs µs (Low Speed) HOLT INTEGRATED CIRCUITS 11 HI-8581 Vcc = 5V, V+ = 10V, V- = -10V, GND = 0V, TA= Oper. Temp. Range and fclk = 1MHz +0.1% with 60/40 duty cycle LIMITS PARAMETER REPEATER OPERATION TIMING Delay - EN LOW to PL LOW Hold - PL HIGH to EN HIGH Delay - TX/R LOW to ENTX HIGH Master Reset Pulse Width ARINC Data Rate and Bit Timing tENPL tPLEN tTX/REN tMR 0 0 0 400 ± 1% ns ns ns ns SYMBOL MIN TYP MAX UNITS HOLT INTEGRATED CIRCUITS 12 HI-8581 ADDITIONAL HI-8581 PIN CONFIGURATION (See page 1 for additional pin configuration) ORDERING INFORMATION PART NUMBER HI-8581PJI HI-8581PJT HI-8581CJI HI-8581CJT HI-8581PQI HI-8581PQT PACKAGE DESCRIPTION 44 PIN PLASTIC J LEAD 44 PIN PLASTIC J LEAD 44 PIN CERQUAD J LEAD 44 PIN CERQUAD J LEAD 44 PIN PQFP 44 PIN PQFP TEMPERATURE RANGE -40°C TO +85°C -55°C TO +125°C -40°C TO +85°C -55°C TO +125°C -40°C TO +85°C -55°C TO +125°C FLOW I T I T I T BURN IN NO NO NO NO NO NO LEAD FINISH SOLDER SOLDER SOLDER SOLDER SOLDER SOLDER HOLT INTEGRATED CIRCUITS 13 HI-8581 PACKAGE DIMENSIONS inches (millimeters) 44-PIN PLASTIC J-LEAD PLCC PIN NO. 1 .045 x 45° PIN NO. 1 IDENT .045 x 45° PACKAGE TYPE: .050 ± .005 (1.27 ± .127) .690 ± .005 (17.526 ± .127) SQ. .653 ± .004 (16.586 ± .102) SQ. .031± .005 (.787 ± .127) .017 ± .004 (.432 ± .102) SEE DETAIL A .009 .011 .172 ± .008 (4.369 ± .203) .610 ± .020 (15.494± .508) DETAIL A .015 ± .002 (.381 ± .051) .020 MIN (.508 ΜΙΝ) R .025 .045 44-PIN CERQUAD J-LEAD Package Type: 2 1 44 43 .688 ± .005 (17.475 ± .127) MAX. SQ. .620 ± .012 (15.748 ± .305) .650 ± .010 (16.510 ± .254) SQ. .039 ± .005 (.990 ± .127) .019 ± .002 (.483 ± .051) .200 MAX. (5.080) .100 ± .007 .050 TYP. (2.540 ± .178) (1.270) HOLT INTEGRATED CIRCUITS 14 HI-8581 PACKAGE DIMENSIONS inches (millimeters) 44-PIN PLASTIC QUAD FLAT PACK (PQFP) Package Type: 44PQS .007 MAX. (.17) .0315 BSC (.80 BSC) .547 ± .010 (13.90 ± .25) SQ. .394 ± .004 (10.0 ± .10) SQ. .014 ± ..002 (.35 ± .05) .035 +.006 / -.004 (.88 +.15 / -.10) See Detail A .097 MAX. (2.45) .079 +.004 / -.006 (2.00 +.10 / -.15) .012 TYP. (.30 R) 0° ≤ Θ ≤ 7° .008 TYP. (.20 R) Detail A H OLT INTEGRATED CIRCUITS 15