Z86C34 Datasheet, PDF (26/70 Pages) Zilog, Inc. – CMOS Z8 MCUs WITH ASCI UART OFFER EFFICIENT, COST-EFFECTIVE DESIGN FLEXIBILITY

Z86C34/C35/C36/C44/C45/C46
CMOS Z8® MCUs with ASCI UART
PIN FUNCTIONS (Continued)
Port 3 (P37–P30). Port 3 is an 8-bit, CMOS-compatible
port, with four fixed inputs (P33–P30) and four fixed out-
puts (P34–P37). It is configured under software control for
Input/Output, Counter/Timers, interrupt, port handshake,
and Data Memory functions. Port 3, bit 0 input is Schmitt-
triggered, and pins P31, P32, and P33 are standard CMOS
inputs (no Auto Latches). Pins P34, P35, P36, P37 are push-
pull output lines. Low-EMI output buffers can be globally
programmed by the software.
Two onboard 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 Reg-
ister (P3M bit 1). For Interrupt functions, Port 3, bit 0 and
pin 3 are falling edge interrupt inputs. P31 and P32 are pro-
grammable as rising, falling, or both edge triggered inter-
rupts (IRQ register Bits 6 and 7). P33 is the comparator ref-
erence voltage input when in Analog mode. Access to
Counter/Timers 1 is made through P31 (T_IN) and P36
ZiLOG
(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); four external
interrupt request signals (IRQ3–IRQ0); timer input and out-
put signals (T_IN and T_OUT); Data Memory Select (DM, see
Table 10 and Figure 15).
P34 output can be software-programmed to function as a
Data Memory Select (DM). The Port 3 mode register (P3M)
Bit D3,D4 selects this function. When accessing external
Data Memory, the P34 goes active Low; when accessing
external Program Memory, the P34 goes High.
An onboard UART (ASCI) can be enabled by software by
setting the RE and TE bits of the ASCI Control Register A
(CNTLA). When enabled, P30 is the receive input and P37
is the transmit output.
Table 10. Port 3 Pin Assignments
Pin
I/O
CTC1 Analog
Int.
P0 HS P1 HS P2 HS
Ext
UART
P30
IN
IRQ3
RX
P31
IN
T_IN
AN1
IRQ2
D/R
P32
IN
AN2
IRQ0
D/R
P33
IN
REF
IRQ1
D/R
P34
OUT
AN1–OUT
R/D
DM
P35
OUT
R/D
P36
OUT
T_OUT
R/D
P37
OUT
AN2–OUT
TX
Notes:
HS = Handshake Signals
D = DAV
R = RDY
Comparator Inputs and Outputs. Port 3, pins P31 and
P32 each feature a comparator front end. The comparator
reference voltage, pin P33, is common to both comparators.
In analog mode, the P31 and P32 are the positive inputs to
the comparators 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. P34 and P37 outputs
the comparator outputs by software-programming the
PCON Register Bit D0 to 1 (see Figure 16).
Note: The user must add a two-NOP delay after selecting the
P3M bit D1 to 1 before the comparator output is valid.
IRQ0, IRQ1, and IRQ2 should be cleared in the IRQ reg-
ister when the comparator is enabled or disabled.
26
PRELIMINARY
DS007601-Z8X0499