W83C553F Datasheet, PDF (107/159 Pages) Winbond – SYSTEM I/O CONTROLLER WITH PCI ARBITER

W83C553F
Electrical Specifications
Timer Control Register
Function:
The Timer Control Register specifies the counter selection, operating mode, counter byte programming
order and count value size, and whether the counter counts down in a 16-bit or Binary Coded Decimal
(BCD) format. After writing the control word, a new count can be written at any time. The new value
will take effect according to the programmed mode.
Type:
Write Only
Bit Description:
Bits [7:6]:
Bits [5:4]:
Bits [3:1]:
SC[1:0]. These bits select the counter the control word acts upon as shown below.
Bit 7
0
0
1
1
Bit 6
0
1
0
1
Function
Counter 0 select
Counter 1 select
Counter 2 select
Read Back command
RW[1:0]. These bits are the read/write control bits. Actual counter programming is done
through the counter I/O port (40h, 41h, 42h for counters 0, 1 and 2, respectively).
Bit 5
0
0
1
1
Bit 4
0
1
0
1
Function
Counter Latch command
R/W Least Significant Byte (LSB)
R/W Most Significant Byte (MSB)
R/W LSB then MSB
M[2:0]. These bits select one of six possible modes of operation for the counter as shown
below.
Bit 3
0
0
x
x
1
1
Bit 2
0
0
1
1
0
0
Bit 1
0
1
0
1
0
1
Mode
0
1
2
3
4
5
Function
Out signal on end of count (=0)
Hardware retriggerable one shot
Rate generator (divide by n counter)
Square wave output
Software triggered strobe
Hardware triggered strobe
Bit 0:
BCD. When this bit is "0", a binary countdown is used. The largest possible binary count is
216. When this bit is "1", a Binary Coded Decimal (BCD) count is used. The largest BCD
count allowed is 104.
WINBOND SYSTEMS LABORATORY
104