Z84C90_12 Datasheet, PDF (24/56 Pages) Zilog, Inc. – KIO Serial/Parallel Counter/Timer

Z84C90 KIO Serial/Parallel Counter/Timer
Product Specification
17
I/O Register Control Word. When Mode 3 is selected, the Mode Control Word data must
be followed by the loading of the I/O Register Control Word data. This word configures
the I/O Register, which defines which port lines are inputs or outputs. A 1 indicates input,
while a 0 indicates output. this word is required with in Mode 3. See Figure 12.
I/O7 I/O6 I/O5 I/O4 I/O3 I/O2 I/O1 I/O0
0: Sets bit to output
1: Sets bit to input
Figure 12. PIO I/O Register Control Word
PIO Interrupt Control Word. When bits D3 to D0 are loaded with 0111, the command
register functions as the PIO Interrupt Control Word Register. In Mode 3 operation, hand-
shake signals are not used. Interrupts are generated as a logic function of the input signal
levels. The Interrupt Control Word sets the logic conditions and the logic levels required
for generating an interrupt. Two logic conditions or functions are available: AND (if all
input bits change to the active level, an interrupt is triggered) and OR (if any one of the
input bits change to the active logic level, an interrupt is triggered). The user can also pro-
gram which input bits are to be considered as part of this logic function. bit D6 sets the
logic function, bit D5 sets the logic level and bit D4 specifies the mask control word data
to follow. See Figure 13.
D7
1
H/L
D0
0111
Identifies interrupt control word
1 = Mask follows¹
1 = Active High
1 = AND function
1 = Interrupt Function Enable²
Notes:
1. Regardless of the operating mode, setting bit D4 = 1 causes any pending
interrupts to be cleared.
2. The port interrupt is not enabled until the interrupt function enable is
followed by an active M1.
Figure 13. PIO Interrupt Control Word
Mask Control Word. This words sets the Mask Control Register, thus allowing any
unused bits to be masked off. If any bits are to be masked, bit D4 of the Interrupt Control
PS011804-0612
Register Programming