Z80181 Zilog., Z80181 Datasheet - Page 32

• Manufacturer Part Number: Z80181
• Description: SMART ACCESS CONTROLLER (SAC)
• Manufacturer: Zilog.

Zilog
CTC Control Registers
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).
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.
2-32
D7 D6 D5 D4 D3 D2 D1 D0
*
Timer Mode Only
Figure 46. CTC Channel Control Word
Addr: E4h (Ch 0)
E5h (Ch 1)
E6h (Ch 2)
E7h (Ch 3)
For more detailed information, refer to the CTC Technical
Manual.
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.
Control or Vector
Reset
Time Constant
Time Trigger
CLK/TRG Edge Selection
Prescaler Value *
Mode
Interrupt
0 Vector
1 Control Word
0 Continued Operation
1 Software Reset
0 No Time Constant Follows
1 Time Constant Follows
0 Automatic Trigger When
1 CLK/TRG Pulse Starts Timer
0 Selects Falling Edge
1 Selects Rising Edge
1 Value of 256
0 Value of 16
0 Selects Timer Mode
1 Selects Counter Mode
1 Enables Interrupt
0 Disables Interrupt
Time Constant is Loaded
*
S
MART
A
CCESS
C
DS971800500
ONTROLLER
Z80181
SAC
™