Z84C90_12 Datasheet, PDF (26/56 Pages) Zilog, Inc. – KIO Serial/Parallel Counter/Timer

Z84C90 KIO Serial/Parallel Counter/Timer
Product Specification
19
D7 D6 D5 D4 0 0 1 1
Interrupt
1 = Enable interrupt
0 = Disables interrupt
Mode
0 = Selects timer mode
1 = Selects counter mode
Prescaler Value*
0 = Value of 16
1 = Value of 256
CLK/TRG Edge Selection
0 = Selects Falling Edge
1 = Selects Rising Edge
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
Timer Trigger*
0 = Automatic trigger when time
constant is loaded
1 = CLK/TRG pulse starts timer
Figure 16. CTC Channel Control Word
Interrupt Enable. Bit D7 enables the interrupt logic so that an interrupt output (INT) can
be generated at zero count. Interrupts can be programmed in either mode and can be
enabled or disabled at any time.
Mode. Bit D6 selects either Timer Mode or Counter Mode.
Prescale Factor. Bit D5 selected the prescale factor for use in Timer Mode. Either divide-
by-16 or divide-by-256 is available.
Clock/Trigger Edge Selector. Bit D4 selects the active edge of the CLK/TRG input
pulses.
Timer Trigger. Bit D3 selects the trigger mode for timer operation. Either an automatic or
an external trigger can be selected.
Time Constant. Bit D2 indicates that the next word loaded into this register is the time
constant data for the downcounter.
Software Reset. Setting bit D1 indicates a software reset operation.
Time Constant Word. Before a channel can start counting, it must receive a time constant
word. The time constant value can be anywhere between 1 and 256, with 0 being accepted
as a count of 256. See Figure 17.
PS011804-0612
Register Programming