Measurement-computing CIO-PDMAxx Manual do Utilizador descarregar pdf (Página 15)

5.1.4 8254 COUNTER LOAD & READ REGISTERS

COUNTER 0

BASE ADDRESS + 4 304h, 772

D0D1D2D3D4D5D6D7

01234567

COUNTER 1

BASE ADDRESS + 5 305h, 773

D0D1D2D3D4D5D6D7

01234567

COUNTER 2

BASE ADDRESS + 6 306h, 774

D0D1D2D3D4D5D6D7

01234567

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

The counters have 16-bits, each with an 8-bit window, the read / load register. Data is

shifted in 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 in

assembly language or in BASIC or some other high level language.

5.1.5 COUNTER CONTROL REGISTER

BASE ADDRESS + 7 307h, 775

BCDM0M1M2RL0RL1SC0SC1

01234567

WRITE ONLY

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

SC1 SC0 Counter

0 0 0

0 1 1

1 0 2

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 31 32

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Measurement-computing CIO-PDMAxx Manual do Utilizador Página 15