Advantech PCI-1751U, Руководство пользователя

Страница: 32 / 38

PCI-1751U User’s Manual 28
BCD Type
0 Binary counting 16-bits
1 Binary coded decimal (BCD) counting
If you set the module for binary counting, the count can be any number
from 0 up to 65535. If you set it for BCD (Binary Coded Decimal) count-
ing, the count can be any number from 0 to 9999.
If you set both SC1 and SC0 bits to 1, the counter control register is in
read-back command mode. The control register data format then
becomes:
BASE+27 8254 control, read-back mode
Bit D7 D6 D5 D4 D3 D2 D1 D0
Value 1 1 CNT STA C2 C1 C0 X
CNT = 0 Latch count of selected counter(s).
STA = 0 Latch status of selected counter(s).
C2, C1 & C0 Select counter for a read-back operation.
C2 = 1 select Counter 2
C1 = 1 select Counter 1
C0 = 1 select Counter 0
If you set both SC1 and SC0 to 1 and STA to 0, the register selected by
C2 to C0 contains a byte which shows the status of the counter. The data
format of the counter read/write register then becomes:
BASE+24/25/26 Status read-back mode
Bit D7 D6 D5 D4 D3 D2 D1 D0
Value OUT NC RW1 RW0 M2 M1 M0 BCD
OUT Current state of counter output
NC Null count is 1 when the last count written to the counter
register has been loaded into the counting element