Measurement-computing PC104-DAS08 Bedienungsanleitung PDF herunterladen (Seite 16)

The data in the counter read register, and the action taken on the data in a counter

load register, is dependent upon the control code written to the control register.

The counters are 16-bit types, each with an 8-bit window (the read / load

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. You can download a copy from our

WEB site at http://www.computerboards.com/PDFmanuals/82C54.pdf

3.6 COUNTER CONTROL REGISTER

BASE ADDRESS + 7

BCDM0M1M2RL0RL1SC0SC1

01234567

WRITE ONLY

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:

RL1 RL0 OPERATION

0 0 Latch counter.

0 1 Read/load high byte.

1 0 Read/load low byte.

1 1 Read/load low the high byte (word transfer).

M2 to M0 are the counter control operation type bits:

M2 M1 M0 OPERATION TYPE

0 0 0 Change on terminal count.

0 0 1 Programmable one-shot.

0 1 0 Rate generator

0 1 1 Square wave generator

1 0 0 Software triggered strobe.

1 0 1 Hardware triggered strobe.

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

If BCD = 1, then counter data is 4-decade Binary Coded Decimal. (9,999 max)

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Measurement-computing PC104-DAS08 Bedienungsanleitung Seite 16