Z80 Datasheet, PDF (23/330 Pages) Zilog, Inc. – Z80 CPU PERIPHERALS

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Table 2. Channel Control Register
7
6
Interrupt Mode
R/W
R/W
5
Prescaler
Value*
R/W
4
3
CLK/TRG Time
Section Trigger*
R/W
R/W
2
Time
Constant
R/W
1
Reset
R/W
0
Control or
Vector
R/W
Bit Number Field
R/W Value Description
7
Interrupt
R/W 1 Enable Interrupt
0 Disable Interrupt
6
Mode
R/W 1 COUNTER Mode
0 TIMER Mode
5
Prescaler Value* R/W 1 256
0 16
4
CLK/TRG Edge R/W 1 Rising Edge
Section
0 Falling Edge
3
Time Trigger* R/W 1 CLK/TRG Pulse Starts Timer
0 Automatic trigger when time constant is loaded
2
Time Constant R/W 1 Time Constant Follows
0 No Time Constant Follows
1
Reset
R/W 1 Software Reset
0 Continue Operation
0
Control or Vector R/W 1 Control
0 Vector
*TIMER mode only
The Prescaler
The prescaler is an 8-bit device that is used in the TIMER mode only. The
prescaler is programmed by the CPU through the Channel Control register
to divide its input, the System clock (0), by 16 or 256. The output of the
prescaler is then fed as an input to clock the down-counter. Each time that
UM008101-0601
Counter/Timer Channels