Counter Read/Write And Control Registers - Advantech MIC-3716 Manual

D.2 Counter Read/Write and Control Registers
The 82C54 programmable interval timer uses four registers at
addresses BASE + 24(Dec), BASE + 26(Dec), BASE + 28(Dec) and
BASE + 30(Dec) for read, write and control of counter functions.
Register functions appear below:
Register
BASE + 24(Dec)
BASE + 26(Dec)
BASE + 28(Dec)
BASE + 30(Dec)
Since the 82C54 counter uses a 16-bit structure, each section of
read/write data is split into a least significant byte (LSB) and most
significant byte (MSB). To avoid errors, it is important that you make
read/write operations in pairs and keep track of the byte order.
The data format for the control register is as below:
BASE+30(Dec) 82C54 control, standard mode
Bit
Value
D7 D6 D5
SC1 SC0 RW1 RW0 M2 M1 M0 BCD
Function
Counter 0 read/write
Counter 1 read/write
Counter 2 read/write
Counter control word
D4 D3 D2 D1 D0
101