Z89135 Datasheet, PDF (24/66 Pages) Zilog, Inc. – Low-Cost DTAD Controller

Z89135/136 (ROMless)
Low-Cost DTAD Controller
Zilog
PIN FUCTIONS (Continued)
Port 3. (P37-P31). Port 3 is a 7-bit, CMOS-compatible port
with three fixed inputs (P33-P31) and four fixed outputs
(P37-P34). It is configured under software control for in-
put/output, counter/timers, interrupt, and port handshakes.
Pins P31, P32, and P33 are standard CMOS inputs; out-
puts are push-pull.
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 the Port 3 Mode
Register (bit 1). Port 3, pin 3 is a falling edge interrupt in-
put. P31 and P32 are programmable as rising, falling or
both edge-triggered interrupts (IRQ register bits 6 and 7).
P33 is the comparator reference voltage input. Access to
counter/timers 1 is through P31 (T_IN) and P36 (T_OUT).
Handshake lines for Ports 0, 1, and 2 are available on P31
through P36.
Port 3 also provides the following control functions: hand-
shake for Ports 0, 1, and 2 (/DAV and RDY); three external
interrupt request signals (IRQ3-IRQ1); timer input and out-
put signals (T_IN and T_OUT); (Figure 13).
Comparator Inputs. Port 3, Pins P31 and P32 each have
a comparator front end. The comparator reference volt-
age, Pin P33, is common to both comparators. In analog
mode, the P31 and P32 are the positive inputs to the com-
parators and P33 is the reference voltage supplied to both
comparators. In digital mode, pin P33 can be used as a
P33 register input or IRQ1 source.
Pin
I/O
P31
IN
P32
IN
P33
IN
P34
OUT
P35
OUT
P36
OUT
P37
OUT
Notes:
HS = Handshake Signals
D = DAV
R = RDY
CTC1
T_IN
T_OUT
Table 3. Port 3 Pin Assignments
AN IN
AN1
AN2
REF
Int.
IRQ2
IRQ0
IRQ1
P0 HS
D/R
R/D
P1 HS
D/R
R/D
P2 HS
D/R
R/D
EXT
DM
1-24
PRELIMINARY
DS97TAD0300