Z80181 Datasheet, PDF (32/74 Pages) Zilog, Inc. – SMART ACCESS CONTROLLER (SAC™)

Zilog
CTC Control Registers
Z80181
SMART ACCESS CONTROLLER SAC^™
Channel Control Word
This word sets the operating modes and parameters as
described below. Bit D0 must be a “1” to indicate that this
is a Control Word (Figure 46).
For more detailed information, refer to the CTC Technical
Manual.
Addr: E4h (Ch 0)
E5h (Ch 1)
E6h (Ch 2)
E7h (Ch 3)
D7 D6 D5 D4 D3 D2 D1 D0
* Timer Mode Only
Control or Vector
0 Vector
1 Control Word
Reset
0 Continued Operation
1 Software Reset
Time Constant
0 No Time Constant Follows
1 Time Constant Follows
Time Trigger *
0 Automatic Trigger When
Time Constant is Loaded
1 CLK/TRG Pulse Starts Timer
CLK/TRG Edge Selection
0 Selects Falling Edge
1 Selects Rising Edge
Prescaler Value *
1 Value of 256
0 Value of 16
Mode
0 Selects Timer Mode
1 Selects Counter Mode
Interrupt
1 Enables Interrupt
0 Disables Interrupt
Figure 46. CTC Channel Control Word
This register has the following fields:
Bit D7. Interrupt Enable. This bit enables the interrupt logic
so that an internal INT is generated at zero count. Interrupts
are programmed in either mode and may be enabled or
disabled at any time.
Bit D6. Mode Bit. This bit selects either Timer Mode or
Counter Mode.
Bit D5. Prescaler Factor. This bit selects the prescaler
factor for use in the timer mode. Either divide-by-16 or
divide-by-256 is available.
Bit D4. Clock/Trigger Edge Selector. This bit selects the
active edge of the CLK/TRG input pulses.
Bit D3. Timer Trigger. This bit selects the trigger mode for
timer operation. Either automatic or external trigger may be
selected.
Bit D2. Time Constant. This bit indicates that the next word
programmed is time constant data for the downcounter.
Bit D1. Software Reset. Writing a “1” to this bit indicates a
software reset operation, which stops counting activities
until another time constant word is written.
2-32
DS971800500