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
Chrontel CH9294
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
Note: The Chrontel and the ST49c214-25 uses pin 3 as Memory Frequency select 2
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 -9
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 40.000
VCLK 3: 36.000 80.000 44.900 40.000 72.000 65.000 32.500 EXCLK
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 55.000
MCLK 1: 35.600 44.347 40.000 24.000 41.612 35.600 63.830 75.000
MCLK 2: 43.900 37.500 45.000 50.000 44.744 43.900 60.000 70.000
MCLK 3: 49.100 44.773 50.000 66.667 50.000 49.100 81.000 80.000
ICS2494 -266 -247 -240 -275 -305 -260
ST49c214 -10 -16 -17 -18 -19 -20 -25
CH9294 -G
VCLK 0: 30.250 XTAL 25.175 25.175 25.175 50.350 25.175
VCLK 1: 65.000 16.257 28.322 28.322 28.322 56.644 28.322
VCLK 2: 85.000 EXCLK 28.626 40.000 40.000 33.250 40.000
VCLK 3: 36.000 32.514 36.000 EXCLK EXCLK 52.000 72.000
VCLK 4: 25.175 25.175 40.000 50.000 50.000 80.000 50.000
VCLK 5: 28.322 28.322 42.954 77.000 77.800 63.000 77.000
VCLK 6: 34.000 24.000 44.900 36.000 36.000 EXCLK 36.000
VCLK 7: 40.000 40.000 57.272 44.889 44.889 75.000 44.900
VCLK 8: 44.900 XTAL 60.000 130.000 130.000 25.175 130.000
VCLK 9: 50.350 16.257 63.960 120.000 120.000 28.322 120.000
VCLK A: 31.500 EXCLK 75.000 80.000 80.000 31.500 80.000
VCLK B: 32.500 36.000 80.000 31.500 31.500 36.000 31.500
VCLK C: 63.000 25.175 85.000 110.000 110.000 40.000 110.000
VCLK D: 72.000 28.322 99.000 65.000 65.000 44.900 65.000
VCLK E: 75.000 24.000 102.000 75.000 75.000 50.000 75.000
VCLK F: 80.000 40.000 108.000 94.500 94.500 65.000 94.500
MCLK 0: 36.000 31.000 64.000 45.000 55.000 40.000 55.000
MCLK 1: 44.000 36.000 40.830 38.000 75.000 33.333 65.000
MCLK 2: 49.000 43.000 48.000 52.000 70.000 44.000 70.000
MCLK 3: 40.000 49.000 60.000 50.000 80.000 50.000 80.000
MCLK 4: 45.000
MCLK 5: 40.000
MCLK 6: 60.000
MCLK 7: 50.000
ICS2494 -261
ATI18811 -0 -1
OTI068 -501 -307
VCLK 0: 42.950 100.000 25.175 25.175
VCLK 1: 48.770 126.000 28.322 28.322
VCLK 2: 92.400 92.400 65.0 65.0
VCLK 3: 36.000 36.000 44,9 44.9
VCLK 4: 50.350 50.350 14.1 28.1
VCLK 5: 56.640 56.640 18.1 36.0
VCLK 6: 0? 0? 40.0 40.0
VCLK 7: 44.900 44.900 36.3 36.0
VCLK 8: 30.240 135.000
VCLK 9: 32.000 32.000
VCLK A 110.000 110.000
VCLK B: 80.000 80.000
VCLK C: 39.910 39.910
VCLK D: 44.900 44.900
VCLK E: 75.000 75.000
VCLK F: 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 16closk mode the External Clock
Input (pin 4) 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:
ICS1394 -073
ST49c394 -24 -30
Trident: 9001 9002 9004
Chrontel: -593
VCLK 0: XTAL 25.175 14.318 25.175 25.175 25.275 25.175
VCLK 1: 16.257 28.322 16.257 28.322 28.322 28.322 28.322
VCLK 2: EXTFREQ 32.514 FREQ0 44.900 44.900 44.900...40.0
VCLK 3: 32.514 36.000 32.514 36.000 36 000 36.000 80.0
VCLK 4: 25.175 40.000 25.175 57.272 57.272 57.272 50.1
VCLK 5: 28.322 44.900 28.322 65.000 65.000 65.000 77.0
VCLK 6: 24.000 65.000 24.000 50.350 50.350 50.350 36.1
VCLK 7: 40.000 84.000 40.000 40.000 40.000 40.000 44.9
VCLK 8: 25.175 25.175 14.318 25.175 88.000 80.0
VCLK 9: 28.322 28.322 16.257 28.322 98.000 119.9
VCLK A: 36.000 40.000 FREQ0 118.000 130.1
VCLK B: 65.000 44.900 36.000 44.900 108.000 31.5
VCLK C: 44.900 32.514 25.175 72.000 72.000 110.1
VCLK D: 50.000 28.322 28.322 77.000 77.000 64.9
VCLK E: 56.000 36.000 24.000 80.000 80.000 74.9
VCLK F: 75.000 65.000 40.000 75.000 75.000 72.3
VCLK 10: 25.175 25.175 14.318
VCLK 11: 28.322 28.322 65.028
VCLK 12: 40.000 32.514 FREQ0
VCLK 13: 65.000 36.000 36.000
VCLK 14: 44.900 40.000 25.175
VCLK 15: 50.000 44.900 28.322
VCLK 16: 56.000 56.000 24.000
VCLK 17: 75.000 65.000 40.000
VCLK 18: 25.175 25.175 44.900
VCLK 19: 28.322 28.322 50.344
VCLK 1A: EXTFREQ 32.514 16.257
VCLK 1B: EXTFREQ 40.000 32.514
VCLK 1C: 60.000 44.900 56.644
VCLK 1D: 80.000 60.000 20.000
VCLK 1E: EXTFREQ 80.000 50.000
VCLK 1F: EXTFREQ 84.000 80.000
ICS90c64
Startech ST49c064
20pin mask-programmable video and memory clock generator
Pins:
1 i Clock input. Typically 14.318 MHz
2 i MA2. Memory clock select 2
3 i External clock input (EXCLK)
4 i A1. Video clock select 1
5 i A0. Video clock select 0
6 i Latch inputs (A0-A3, MA0-MA2) on rising edge
7 i A2. Video clock select 2
8 i A3. Video clock select 3
9 i MA0. Memory clock select 0
10 o Digital ground
11 i MA1. Memory clock select 1
12 o MCLK. Memory clock output
14 i MCLK output enable
15 i Analog VCC
16 o Analog ground
18 i DCLK output enable
19 o DCLK. Video clock output
20 i Digital VCC
ST49c064 -? -?
ICS9064 -?
AV9064 -?
VCLK 0: 30.000 30.000
VCLK 1: 77.250 77.250
VLKC 2: EXCLK EXCLK
VCLK 3: 80.000 80.000
VCLK 4: 31.500 31.500
VCLK 5: 36.000 36.000
VCLK 6: 75.000 75.000
VCLK 7: 50.000 50.000
VCLK 8: 40.000 40.000
VCLK 9: 50.000 50.000
VCLK A: 32.000 32.000
VCLK B: 44.900 44.900
VCLK C: 25.275 25.275
VCLK D: 28.322 28.322
VCLK E: 65.000 65.000
VCLK F: 36.000 36.000
MCLK 0: 33.000 41.612
MCLK 1: 49.218 37.500
MCLK 2: 60.000 49.128
MCLK 3: 30.500 44.296
MCLK 4: 41.612
MCLK 5: 37.500
MCLK 6: 49.128
MCLK 7: 44.296
IC Designs ICD2061,ICD2061A
ICS 9161
Diamond DCS2824
The ICD2062 appears very similar
16 pin user programmable video and memory clock generator.
Pins:
1 i SEL0/CLK. In programming mode the clock input, in normal mode selects
the clock together with SEL1.
2 i SEL1/DATA In programming mode the data input, in normal mode selects
the clock together with SEL0.
3 i AVDD. +5V Analog
4 i OUTDIS-. Output disabled if low.
5 Ground.
6 i Reference crystal (typically 14.31818MHz)
7 o Crystal out
8 o Memory Clock output
9 o Video Clock output
10 o Error Output, Low if an error occured in the serial programming
11 i Feature Clock input
12 i INIT0. Selects initial state
13 i VDD. +5V
14 i INIT1. Selects initial state
15 i INTCLK
16 i PWRDWN
The initial frequencies are selected by INIT0 and INIT1:
INIT0 INIT1 MREG REG0 REG1 REG2
0 0 32.500 25.175 28.322 28.322
0 1 40.000 25.175 28.322 28.322
1 0 50.350 40.000 28.322 28.322
1 1 56.644 40.000 50.350 50.350
Note: some versions might have different power on values.
The Memory Clock output is controlled by the MREG register.
The Video Clock output is controlled by REG0-2 and the Feature Clock:
INTCLK SEL1 SEL0 Video Clock:
x 0 0 REG0
x 0 1 REG1
0 1 0 Feature Clock
1 1 0 REG2
x 1 1 REG2
x = Don't care.
There are 6 24bit registers:
REG0 Video Clock Register 1
REG1 Video Clock Register 2
REG2 Video Clock Register 3
MREG Memory or I/O Timing Register
bit 0-6 Q Counter. Actual Q value is 2 higher (Ie. 2..129)
7-9 Post VCO divider (M). Divide output clock by
0: 1, 1: 2, 2: 4, 3: 8, 4: 16, 5: 32, 6: 64, 7: 128
10-16 P Counter. Actual P value is 3 higher (Ie. 3..130)
17-20 Index. Selects the VCO range (in MHz):
0: 50.0-51.0 1: 51.0-53.2 2: 53.2-58.5 3: 58.5-60.7
4: 60.7-64.4 5: 64.4-66.8 6: 66.8-73.5 7: 73.5-75.6
8: 75.6-80.9 9: 80.9-83.2 10: 83.2-91.5 11: 91.5-100.0
12-15: 100.0-120.0
For the Video Clocks (REG0-2):
14 turns off VCLK and 15 sets VCLK to MCLK
21-23 Selects the register: 0: REG0, 1: REG1, 2: REG2, 3: MREG
Output clock is (Pre*Ref*(P/Q))/M
Where Pre is the prescale factor, usually 2 but can be set to 4 on
the ICD2061A (REG0-2 only) in the control register. Ref is the
reference clock typically 14.31818MHz.
The
PWRDWN Divisor for Power-Down mode.
bit 17-20 Powerdown divisor. When in Power down mode 1 the Memory
Clock is set to the reference crystal/the value below.
1: 32, 2: 30, 3: 28, 4: 26, 5: 24, 6: 22, 7: 20, 8: 18
9: 16, 10: 14, 11: 12, 12: 10, 13: 8, 14: 6, 15: 4
Power on default is 8 I.e. divide by 18.
21-23 Always 4 to select Power down register
CNTL Control Register
bit 12 (not 2061) P Counter Prescale (REG0). If set REG0 uses a
prescale factor (Pre) of 4, if clear Pre = 2
13 (not 2061) P Counter Prescale (REG1). If set REG1 uses a
prescale factor (Pre) of 4, if clear Pre = 2
14 (not 2061) P Counter Prescale (REG2). If set REG2 uses a
prescale factor (Pre) of 4, if clear Pre = 2
16 Duty Cycle Adjust. If set causes the clock high period to
be 1ns shorter than normally.
18 Timeout Interval. Defines the timeout period for clock
selection and VCO settle. Set for twice normal timeout.
19 MUXREF. Selects the clock to output on VCLKOUT during
frequency changes. Set for MCLK, clear for f(ref).
20 Power-Down Mode. Set for Power-Down Mode 2 (Xtal
oscillator shutdown), clear for Power-Down Mode 1
(MCLKOUT = PWRDWN Divisor).
21-23 Always 6 to select Control register
All undefined bits must be set to 0.
To program a clock value:
CLK DATA
1 1 !repeat these two 6 times
0 1 !
0 0
1 0
0 0 !Start bit
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 !Stop bit
1 1
Sierra SC11412 Programmable dual clock generator.
The SC11412 has a 20bit command word. The chip is controlled by 3 control pins
One pin selects either programming mode (1) or operating mode (0).
The two other pins
Pins:
? i Program/Run. When high the chip is in programming mode, when low in
run mode.
? i Clksel0/Data. If run mode the low bit of the two clock select bits. In
programming mode the data line. Typically driven from bit 2 of the
Misc Output register at 3C2h.
? i Clksel1/Clk. If run mode the high bit of the two clock select bits. In
programming mode the clock line. Typically driven from bit 3 of the
Misc Output register at 3C2h.
Command word:
Bit 0 Selects the clock to program. 0: Memory Clock, 1: Pixel clock
1 Enable output driver 0 for programming, 1 for reading ?
2 Enable VCO (0?)
3 External frequency programming mode (0?)
4-5 Divider (D). 0: /1, 1: /2, 2: /4, 3: /8
6-12 N. Multiplier (3 - 127)
13-19 M. (2 - 127)
The resultant clock is N/(M* 2^D) *Quarts Freq (typically 14.318MHz).
The frequency before the 2^D factor is applied must be between 45 and 100MHz
To program the chip use the following sequence:
Prog/Run Clock Data
1 0 0
1 0 data ! Repeat for each of the 20 data bits, starting
1 1 data ! with bit 0.
0 1 0 ! Use 0 1 0 to select the Pixel clock
A delay of a few microseconds between each step might be needed.
ICS 2595 Programmable Clock generator.
The ICS2595 uses 5 control pins for selecting and programming 16 clocks
The ICS2595 has a 20 bit control word:
Bit 0 Start bit. Must be 0.
1 R/W Control. 0: Write, 1: Read
2-6 Location. Selects the clock to reprogram.
7-14 N. Multiplier. App 256 - 465?. Stored as 257 less, i.e 256 is stored
as 255, 257 as 0 and 465 as 208.
15 EXTFREQ. 0 to disable external clock
16-17 Divider (D). 0: /1, 1: /2, 2: /4, 3: /8
18-19 Stop bits, both 1.
The resulting clock is calculated as: basefreq * N/(46 *2^D)
CLK0 CLK1 CLK2 CLK3 CLK4
0 0 0 0 0
0 0 0 0 1
0 0 0 0 0
1 0 0 0 1
1 0 0 0 0
0 0 data 0 1 !Repeat for each bit of the control word,
0 0 data 0 0
0 0 data 1 1 ! starting with bit 0.
0 0 data 1 0
0 0 0 0 0
Other Clock chips:
MX8602 (Used on MXIC cards)
ICD2042ASC (Used on Compaq QVision)
HM8694P (Used on HMC cards)