ZT 88CT08A/88CT09A CMOS Boards
Slowing down the processor clock is useful for power-critical
applications that don’t always require full speed processing. For
example, a situation may exist in which processing occurs only during
certain time intervals. The software can slow down the clock for non-
critical processing times, yet continue to process in order to monitor
non-critical events such as checking time of day.
This feature is provided by the 82C85 clock chip supplied on the
ZT 88CT08A and ZT 88CT09A boards.
An input to this chip
determines the speed of the clock it supplies to the CPU. You can
alter the processor clock speed either in software through a printer
port output or in hardware through jumper W46. The printer port bit
Select In (SLIN*) controls the speed of the processor clock only if
jumper W46B is installed; SLIN* is at address 037Ah, bit 3.
Definition of this bit is as follows:
SLIN* = 0
Full Processor Speed (5 or 8 MHz)
SLIN* = 1
Processor Speed Divided by 256 (19.5 or 31.25 kHz)
Note: SLIN* is also used to enable the lower 128K of a 256K
EPROM installed in socket 5D1. Refer to Chapter 9, "Centronics
Printer Interface."
If you use Ziatech printer cable ZT 90039 or equivalent to interface to
the printer, this bit is free to control processor speed even if a printer
is being used. This is because the signal is one of four used for on-
board resources and is not driven to the printer. Refer to Chapter 9,
"Centronics Printer Interface," for further details on shared printer
port signals.
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