ICS82C404 Datasheet, PDF (7/13 Pages) Integrated Circuit Systems – Dual Programmable Graphics Frequency Generator

ICS82C404
Power Management Issues
Power-down mode 1
The ICS82C404 contains a mechanism to reduce the quiescent
power when stand-by operation is desired. Power-down mode
1 is invoked by pulling PD low and having the proper CNTL
register bit set to zero. In this mode, VCOs are shut down, the
VCLK output is forced high, and the MCLK output is set to a
user-defined low frequency value to refresh dynamic RAM.
The power-down MCLK value is determined by the following
equation:
MCLKPD=FREF/(PWRDWN register divisor value)
The power-down register divisor is determined according to
the 4-bit word programmed into the PWRDWN register (see
table below).
Power-down Mode 2
When there is no need for any output during power-down, an
alternate mode is available which will completely shut down
all outputs and the reference oscillator, but still preserves all
register contents. Power-down mode 2 is invoked by the first
programming the power-down bit in the CNTL register and
then pulling the PD pin low.
The PD pin
The PD pin has a standard internal pull-up resistor during
normal operation. When the chip goes into power-down mode
1 or 2, the normal pull-up resistor is dynamically switched to
a weak pull-up, which reduces power consumption. If the PD
pin is allowed to float after it has been pulled down, the weak
pull-up will bring the signal high and allow the device to
resume operation.
Power-Down Register Table
PWRDWN bits
P3
P2
P1
P0
0
0
0
0
0
0
0
1
0
0
1
0
0
0
1
1
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
1
0
0
1
1
0
1
0
1
0
1
1
1
1
0
0
1
1
0
1
1
1
1
0
1
1
1
1
PWRDWN
Register Value
0
1
2
3
4
5
6
7
8 (default)
9
A
B
C
D
E
F
Power-down
Divisor
n/a
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
MCLKPD
(fREF=14.31818)
n/a
447.4 kHz
477.3 kHz
511.4 kHz
550.7 kHz
596.6 kHz
650.8 kHz
715.9 kHz
795.5 kHz
894.9 kHz
1.02 MHz
1.19 MHz
1.43 MHz
1.79 MHz
2.39 MHz
3.58 MHz
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