Chapter 7 Programmable Pacer 45
7.2 Counter Read/write and Control
Register
The 8254 programmable interval timer uses four registers at addresses
BASE+12, BASE+13, BASE+14 and BASE+15. Register functions
are listed below:
Register
Function
BASE+12
Counter 0 read/write
BASE+13
Counter 1 read/write
BASE+14
Counter 2 read/write
BASE+15
Counter control word
Since the 8254 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 appears below:
BASE+15 - 8254 control, standard mode
Bit
D7
D6
D5
D4
D3
D2
D1
D0
Value SC1
SC0
RW1
RW0
M2
M1
M0
BCD
SC1 & SC0
Select counter
Counter
SC1
SC0
0
0
0
1
0
1
2
1
0
Read-back command
1
1
Summary of Contents for 3718HG
Page 1: ...PCM 3718H 3718HG PC 104 12 bit DAS Module with Programmable Gain User s manual ...
Page 2: ......
Page 5: ...1 General Information CHAPT ER ...
Page 13: ...2 Installation CHAPT ER ...
Page 21: ...3 Signal Connections CHAPT ER ...
Page 26: ...22 PCM 3718H 3718HG User s Manual ...
Page 27: ...4 Register Structure and Format CHAPT ER ...
Page 38: ...34 PCM 3718H 3718HG User s Manual ...
Page 39: ...5 A D Conversion CHAPT ER ...
Page 45: ...6 Digital Input Output CHAPT ER ...
Page 47: ...7 Programmable Pacer CHAPT ER ...
Page 57: ...8 Direct Memory Access Operation CHAPT ER ...
Page 60: ...56 PCM 3718H 3718HG User s Manual ...
Page 61: ...9 Calibration CHAPT ER ...
Page 64: ...60 PCM 3718H 3718HG User s Manual ...