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Computer Group Literature Center Web Site
Functional Description
3
M48T559 Watchdog Timer
The M48T559 contains one Watchdog timer. This Watchdog timer output
is logically ORed with the Raven Watchdog timer 2 output to provide a
hard reset. Refer to the device data sheet and the MCP750 Programmer’s
Reference Guide (MCP750A/PG) for programming information.
Interval Timers
The PBC has three built-in counters that are equivalent to those found in
an 82C54 programmable interval timer. The counters are grouped into one
timer unit, Timer 1, in the PBC. Each counter output has a specific
function:
❏
Counter 0 is associated with interrupt request line IRQ0. It can be
used for system timing functions, such as a timer interrupt for a
time-of-day function.
❏
Counter 1 generates a refresh request signal for ISA memory. This
timer is not used in the MCP750.
❏
Counter 2 provides the tone for the speaker output function on the
PBC (the
SPEAKER_OUT
signal which can be cabled to an external
speaker via the transition module).
The interval timers use the OSC clock input as their clock source. The
MCP750 drives the OSC pin with a 14.31818MHz clock source.
16-Bit Timers
Three 16-bit timers, provided by the Z8536 CIO device, are available on
the MCP750. For information on programming these timers, refer to the
data sheet for the Z8536 CIO device, listed in
Appendix B, Related
Documentation
.
