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WR*
IACK*
10 WRITE* permits the CPU to write control data to
8259A control register.
Is supplied by the CPU and other logic elements.
Transfers one byte for each of two IACK* pulses.
Only the second byte is used to provide an 8-bit
interrupt vector.
The INT output from the 8259A goes to the ArnZ8002 VI* input via
inverter U58.
SYSTEM TIMING CONTROLLER
The Arn9513 System Timing Controller provides five 16-bit general
purpose counters, each with a load register and a hold register.
Counters 1 and 2 each have a 16-bit comparator and an alarm register
and can function in a 24-hour clock mode.
In addition, the Am9513
contains a 16-bit
counter/frE~quency
scaler and a 4-bit counter/FOUT
divider.
All counters except the FOUT divider can operate either in a
binary or BCD mode.
Each of the five 16-bit counters has an output
pin, gate pin, and a source pin associated with it.
Cont ro 1 of the Am9513 is by means of four cont ro 1 1 i nes •
Data and
control programmi ng between the Arn9513 and CPU is over a 16-b it data
bus.
The following is a description of the four control lines:
CS*
TIMER CE* enables the Am9513 whenever timer/CPU
operations take place.
C/O
ASl is address bit 1.
When AB1 is high, the
control and status registers are available to the
CPU.
When
AB1
is
low,
data
regi sters
are
accessible to the CPU.
RD*
10 READ* permi ts readi ng of status regi sters or
data from the Arn9513, dependi ng on the state of
AS1.
WR*
10 WRITE* permits writing of control words or data
to the Am9513, depending on the state of AB1.
The FOUT pi n of the Arn9513 is used to provi de the baud rate clock for
the two Am9551 serial I/O devices.
The clock source for the Am9513 is
a 2.4576 MHz signal derived from a 19.6608 MHz oscillator.
The 2.4576
MHz signal is divided by 16 whenever the Am9513 is reset or power is
applied, and" available at FOUT.
The 2.4576 MHz signal divided by 16 to
produce 16 x 9600 baud.
Also, counters 3 and 4 can be used to provide
programmab
1
e
baud
rates
by
connect i ng
the
proper
jumpers
and
programming the appropriate load register.
Programming information is
available in chapter 3.
All of the inputs, outputs, and gate inputs
for the fi ve general purpose counters are ava i
1
ab
1
e at connector P2.
Jumpers 188 and 189 are available when the 24 hour clock function is
des"i red.
4-10
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