Measurement-computing CIO-DAS08-PGH User Manual download pdf (Page 21)

4.5 COUNTER LOAD & READ REGISTERS

COUNTER 0

BASE ADDRESS + 4 (Read / Write)

D0D1D2D3D4D5D6D7

01234567

COUNTER 1

BASE ADDRESS + 5 (Read / Write)

D0D1D2D3D4D5D6D7

01234567

COUNTER 2

BASE ADDRESS + 6 (Read / Write)

D0D1D2D3D4D5D6D7

01234567

The data in the counter read register, and the action taken on the data in a counter load register, is wholly dependent upon the

control code written to the control register.

The counters are 16-bit counters, each with an 8-bit window, the read / load register. Data is shifted into and out of the 16-bit

counters through these 8-bit windows according to the control byte.

You will need an 8254 data sheet if you want to program the 8254 directly at the register level.

4.6 COUNTER CONTROL REGISTER

BASE ADDRESS + 7 (Write Only)

BCDM0M1M2RL0RL1SC0SC1

01234567

WRITE

SC1 to SC0 are the counter select bits. They are binary coded between 0 and 2.

RL1 to RL0 are the read and load control bits:

Read/load low the high byte (word transfer)11

Read/load low byte01

Read/load high byte10

Latch Counter00

OPERATIONRL0RL1

M2 to M0 are the counter control operation type bits:

Hardware triggered strobe101

Software triggered strobe001

Square wave generator110

Rate generator010

Programmable one-shot100

Change on terminal count000

OPERATION TYPEM0M1M2

BCD = 0 then counter data is 16-bit binary. (65,535 max)

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 27 28

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Measurement-computing CIO-DAS08-PGH User Manual Page 21