Clock Circuits Early boards used discrete clock crystals since there typically were only 2-4, but as newer boards can require more than a dozen frequencies, an integrated clock circuit is often used. Another option is to have the clock circuitry on-chip as with the Cirrus Logic CL-GD54xx series. VCLK refers to Video Clock and MCLK refers to Memory Clock. ICS90c61A Startech ST49c061 20pin mask-programmable combined video and memory frequency generator. Pins: 1 i Reference Clock Input for 14.318MHz reference crystal. 2 i Feature Clock Input. 3 i External Clock Input. 4 i Video Frequency Select bit 0 5 i Video Frequency Select bit 1 6 i Address Latch Enable. Set low to latch new frequency selectors. 7 i VGATTL. Video Frequency Select bit 2. 8 i FCLKSEL. If low the Feature Clock Input (pin 2) is used as the video clock 9 i Memory Frequency Select bit 0. 10 o Digital Ground 11 i Memory Frequency Select bit 1. 12 o Memory Clock Output. 14 i Memory Clock Output Enable. 15 i Analog Supply Voltage. Single +5V. 16 o Analog Ground. 18 i Video Clock Output Enable. 19 o Video Clock Output. 20 i Digital Supply Voltage. Single +5V. The memory clock is one of four programmed frequencies selected by pins 9 & 11 The video clock is one of eight programmed frequencies selected by pins 4,5 and 7, or the Feature Clock Input (pin2) if pin 8 is low. The programmed clocks are calculated as: (Reference clock *A)/(B*C) Where A is 1..127, B is 1..127 and C is 1,2 or 4. As this chip is mask programmable many versions exist: ICS90c61A -PR1 -PR2 ST49c061 -01 -02 Video Clk 0: REF REF Video Clk 1: 16.256 16.108 Video Clk 2: 32.000 32.216 Video Clk 3: 44.900 44.744 Video Clk 4: 25.175 25.057 Video Clk 5: 28.322 28.089 Video Clk 6: 65.000 EXTRN Video Clk 7: 36.000 36.242 Memory Clk 0: 40.000 41.612 Memory Clk 1: 37.500 37.585 Memory Clk 2: 36.000 36.242 Memory Clk 3: 44.900 44.744 ICS2494 Startech ST49c214 ATI 18811 20pin mask-programmable combined video and memory frequency generator. Pins: 1 i Crystal or external clock input. Usually 14.318MHz 2 o Crystal output. 3 i External Clock 4 i Video Frequency Select bit 0 5 i Video Frequency Select bit 1 6 i Address Latch Enable. Set high to latch new clock selectors. 7 i Video Frequency Select bit 2 8 i Video Frequency Select bit 3 9 i Memory Frequency Select bit 0 10 o Digital and Analog ground 11 i Memory Frequency Select bit 1 12 o Memory Clock Output. 13 i Digital Supply Voltage. Single +5V 14 o Digital and Analog ground 15 i Analog Supply Voltage. Single +5V 16 o Digital and Analog Ground 17 o Digital and Analog Ground 18 o Buffered Crystal Clock Output Frequency 19 o Video Clock Output 20 i Digital Supply Voltage. Single +5V The memory clock is one of four programmed frequencies selected by pins 9 & 11 The video clock is one of sixteen programmed frequencies selected by pins 4,5, 7 and 8. Also the External Clock Input (pin 3) can be used. The programmed clocks are calculated as: (Reference clock *A)/(B*C) Where A is 1..127, B is 1..127 and C is 1,2 or 4. As this chip is mask programmable many versions exist: ICS2494 -236 -242 -231 -244 -237 -253 -256 ST49c214 -1 -2 -3 -4 -5 -6 -8 VCLK 0: XTAL 30.000 25.175 20.000 50.350 25.175 25.175 25.175 VCLK 1: 65.028 77.250 28.325 24.000 56.644 28.322 28.322 28.322 VCLK 2: EXTRN EXTRN 85.000 32.000 65.000 40.000 40.000 0 ? VCLK 3: 36.000 80.000 44.900 40.000 72.000 65.000 32.500 0 ? VCLK 4: 25.175 31.500 40.000 50.000 80.000 44.900 50.000 50.000 VCLK 5: 28.322 36.000 48.000 66.667 89.800 50.000 65.000 77.000 VCLK 6: 24.000 75.000 50.000 80.000 63.000 130.000 38.000 36.000 VCLK 7: 40.000 50.000 81.150 100.000 75.000 75.000 44.900 44.900 VCLK 8: 44.900 40.000 25.175 54.000 25.175 25.175 31.500 130.000 VCLK 9: 50.350 50.000 28.325 70.000 28.322 28.322 36.000 120.000 VCLK A: 16.257 32.000 37.500 90.000 31.500 EXTRN 80.000 80.000 VCLK B: 32.514 44.900 44.900 110.000 36.000 EXTRN 63.000 31.500 VCLK C: 56.644 25.175 40.000 25.000 40.000 60.000 50.000 110.000 VCLK D: 20.000 28.322 32.500 33.333 44.900 80.000 100.000 65.000 VCLK E: 41.539 65.000 50.000 40.000 50.000 EXTRN 76.000 75.000 VCLK F: 80.000 36.000 65.000 50.000 65.000 EXTRN 110.000 72.000 MCLK 0: 32.900 36.000 36.000 16.000 40.000 32.900 70.000 MCLK 1: 35.600 44.347 40.000 24.000 41.612 35.600 63.830 MCLK 2: 43.900 37.500 45.000 50.000 44.744 43.900 60.000 MCLK 3: 49.100 44.773 50.000 66.667 50.000 49.100 81.000 ICS2494 -275 -305 -261 ATI18811 -0 -1 VCLK 0: 25.175 25.175 42.950 100.000 VCLK 1: 28.322 28.322 48.770 126.000 VCLK 2: 40.000 40.000 92.400 92.400 VCLK 3: 0 ? 0? 36.000 36.000 VCLK 4: 50.000 50.000 50.350 50.350 VCLK 5: 77.000 77.000 56.640 56.640 VCLK 6: 36.000 36.000 0? 0? VCLK 7: 44.900 44.900 44.900 44.900 VCLK 8: 130.000 130.000 30.240 135.000 VCLK 9: 120.000 120.000 32.000 32.000 VCLK A 80.000 80.000 110.000 110.000 VCLK B: 31.500 31.500 80.000 80.000 VCLK C: 110,000 110.000 39.910 39.910 VCLK D: 65.000 65.000 44.900 44.900 VCLK E: 75.000 75.000 75.000 75.000 VCLK F: 94.500 94.500 65.000 65.000 MCLK 0: MCLK 1: MCLK 2: MCLK 3: Special version such as the OAK OTI068 and UMC UM9502 exist ICS1394 Startech ST49c394 Trident TCK900x 20pin mask-programmable video frequency generator. Pins: 1 i Frequency Select bit 3 2 i Address Latch Enable. Set high to latch new selectors. 3 i Digital Supply Voltage. Single +5V 4 i Frequency Select bit 4 or external clock input 1 5 i Crystal or external clock input. 6 o Crystal output 7 i External Clock Input 2 8 o Digital Ground 9 o Video Clock Output 12 i Analog Supply Voltage. Single +5V 17 o Analog Ground 18 i Frequency Select bit 0 19 i Frequency Select bit 1 20 i Frequency Select bit 2 The video clock is one of 16 or 32 programmed frequencies selected by pins 18,19,20,1 and possibly 4. If the chip is in 16Also the External Clock Input (pin 3) can be used. The programmed clocks are calculated as: (Reference clock *A)/(B*C) Where A is 1..127, B is 1..127 and C is 1,2 or 4. As this chip is mask programmable many versions exist: ST49c394 -24 -30 Trident: 9001 9002 9004 VCLK 0: 25.175 14.318 25.175 25.175 25.275 VCLK 1: 28.322 16.257 28.322 28.322 28.322 VCLK 2: 32.514 FREQ0 44.900 44.900 44.900 VCLK 3: 36.000 32.514 36.000 36 000 36.000 VCLK 4: 40.000 25.175 57.272 57.272 57.272 VCLK 5: 44.900 28.322 65.000 65.000 65.000 VCLK 6: 65.000 24.000 50.350 50.350 50.350 VCLK 7: 84.000 40.000 40.000 40.000 40.000 VCLK 8: 25.175 14.318 88.000 88.000 VCLK 9: 28.322 16.257 98.000 98.000 VCLK A: 40.000 FREQ0 118.800 118.000 VCLK B: 44.900 36.000 108.000 108.000 VCLK C: 32.514 25.175 72.000 VCLK D: 28.322 28.322 77.000 VCLK E: 36.000 24.000 80.000 VCLK F: 65.000 40.000 75.000 VCLK 10: 25.175 14.318 VCLK 11: 28.322 65.028 VCLK 12: 32.514 FREQ0 VCLK 13: 36.000 36.000 VCLK 14: 40.000 25.175 VCLK 15: 44.900 28.322 VCLK 16: 56.000 24.000 VCLK 17: 65.000 40.000 VCLK 18: 25.175 44.900 VCLK 19: 28.322 50.344 VCLK 1A: 32.514 16.257 VCLK 1B: 40.000 32.514 VCLK 1C: 44.900 56.644 VCLK 1D: 60.000 20.000 VCLK 1E: 80.000 50.000 VCLK 1F: 84.000 80.000 IC Designs ICD2061A Diamond DCS2824 16 pin user programmable clock generator. A (typically 14.318 MHz) crystal is connected to pin 6 & 7. There are two input pins (CLK and DATA) for selecting one of four programmed clocks and for programming a new clock. Pins: 6 ? Reference Clock 7 ? Reference Clock ? i CLK. In programming mode this is the "clock" signal to synchronize the data stream from the DATA pin. In normal mode this is bit 0 of the clock select ? i DATA. In programming mode this is the data signal. Command word: Bit 1-7 m-2. 8-9 Divisor. 0: 1, 1: 2, 2: 4, 3: 8 11-17 n-3. 18-21 Clock index select. 22-23 Register nbr. The actual clock frequency is calculated as: ((((Reference Clock) * n)/m)/divisor Where n is 3..130, m is 2..129 and the divisor is (1,2,4,8) Typically the Reference Clock is 14.318MHz To program a clock value: CLK DATA 0 0 0 1 1 1 !repeat these two 6 times 0 1 ! 0 0 1 0 0 0 1 0 1 ~data ! Repeat for each of 24 bits, starting with 0 ~data ! the least significant 0 data ! data is the data bit 1 data ! ~data is the inverse data bit 1 1 0 1 1 1 Other Clock chips: MX8602 (Used on MXIC cards) ICS90c64 (Used on WD90c33 board) ICS2042ASC (Used on Compaq QVision) HM8694P (Used on HMC cards)