Analog Comparators; Comparator Description - ZiLOG Z8 Series User Manual

Register F7h
Port 3 Mode Register (P3M)
(Write-Only)
0 0

Analog Comparators

Select Z8 devices include two independent on-chip analog comparators. See the device
product specification for feature availability and use. Port 3, Pins P31, and P32 each has a
comparator front end. The comparator reference voltage, pin P33, is common to both com-
parators. 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, P35, or P37 may output the comparator
outputs by software-programming the PCON Register bit D0 to 1.

Comparator Description

Two on-board comparators process analog signals on P31 and P32 with reference to the
voltage on P33. The analog function is enabled by programming the Port 3 Mode Register
(P3M bit 1). For interrupt functions during analog mode, P31 and P32 are programmable
as rising, falling, or both edge triggered interrupts (IRQ register bits 6 and 7).
Note: P33 cannot generate an external interrupt while in this mode. P33 can only generate inter-
rupts in DIGITAL mode.
UM001604-0108
0 0 0 0 0 0
0 Port 2 Open-Drain
1 Port 2 Push–Pull
0 P31, P32 Digital Mode
1 P31, P32 Analog Mode
0 P32 = Input
1 P32 = DAV0/RDY0
00 P33 = Input
01 P33 = Input
10 P33 = Input
11 P33 = DAV1/RDY1 P34 = RDY1/DAV1
0 P31 = Input
1 P32 = DAV2/RDY2
0 P30 = Input
1 P30 = Serial In
0 Parity OFF
1 Parity ON
Figure 56. Port 3 Mode Reset
User Manual
P35 = Output
P35 = RDY0/DAV0
P34 = Output
P34 = DM
P34 = DM
P36 = Output
P36 = RDY2/DAV2
P37 = Output
P37 = Serial Out
Input/Output Ports
®
Z8 CPU
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