Z86C83/C84/E83
Zilog CMOS Z8
®
MCU
DS97DZ80700 P R E L I M I N A R Y 8-25
1
Port 3 (P36-P31) Port 3 is a 6-bit, CMOS-compatible port,
with three fixed inputs (P33-P31) and three fixed outputs
(P34-P36), configured under software control for In-
put/Output, Counter/Timers, interrupt, and port hand-
shake. P31, P32, and P33 are standard CMOS inputs (no
Auto Latches). Pins P34, P35, and P36 are push-pull out-
put lines (Figure 11). Low EMI output buffers can be glo-
bally programmed by the software.
Two on-board comparators can process analog signals on
P31 and P32 with reference to the voltage on P33. The an-
alog function is enabled by programming Port 3 Mode
Register (P3M bit 1). For Interrupt functions, Port 3, pin 3
is falling-edge interrupt input. P31 and P32 are program-
mable as rising, falling, or both edge triggered interrupts
(IRQ register bits 6 and bit 7). P33 is the comparator refer-
ence voltage input when in Analog Mode. Access to
Counter/Timers 1 is made through P31 (T
IN
) and P36
(T
OUT
). Handshake lines for Ports 0 and 2 are available on
P31/P36 and P32/P35 (Table 10).
Port 3 also provides the following control functions: hand-
shake for Ports 0 and 2 (/DAV and RDY); three external in-
terrupt request signals (IRQ2-IRQ0); timer input and out-
put signals (T
IN
and T
OUT
).
Auto Latch. The Auto-Latch instruction puts valid CMOS
levels on CMOS inputs that are not externally driven.
Whether this level is 0 or 1, cannot be determined. A valid
CMOS level, rather than a floating node, reduces exces-
sive supply current flow in the input buffer.
Note: Pins 03, 04, 05, 06 have permanently enabled Auto
Latches.
Comparator Inputs. Port 3, P31 and P32, each have a
comparator front end. The comparator reference voltage,
P33, is common to both comparators. In analog mode, the
P33 input functions as a reference voltage to the compar-
ators. In Analog Mode, the internal P33 register and its cor-
responding IRQ1 is connected to the Stop-Mode Recovery
source selected by the SMR register. In this mode, any of
the Stop-Mode Recovery sources are used to toggle the
P33 bit or generate IRQ1. In Digital Mode, P33 can be
used as a Port 3 register input or IRQ1 source. P34 out-
puts the comparator outputs by software programming the
PCON Register bit D0 to 1.
Note: When enabling/or disabling the analog mode, the
following is recommended:
1. allow two NOP delays before reading the comparator
output
2. disable interrupts, switch to analog mode, clear
interrupts, and then re-enable interrupts.
Table 10. Port 3 Pin Assignments
Pin I/O CTC1 Analog Int. P0 HS P2 HS
P31 IN T
IN
AN1 IRQ2 D/R
P32 IN AN2 IRQ0 D/R
P33 IN REF IRQ1
P34 OUT AN1-OUT
P35 OUT R/D
P36 OUT T
OUT
R/D
Notes:
HS = Handshake Signals
D = /DAV
R = RDY
