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)