Intel 87C196CA, Supplement To User’S Manual

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5-1
CHAPTER 5
I/O PORTS
The I/O ports of the 8XC196Lx are functionally identical to those of the 8XC196Jx. However, on
the 87C196LA and LB, the reset state level of all 41 general-purpose I/O pins has changed from
a weak logic “1” (wk1) to a weak logic “0” (wk0). This chapter outlines the differences between
the 87C196LA, LB and the 8XC196Kx controllers.
5.1 I/O PORTS OVERVIEW
Table 5-1 provides an overview of the 8XC196Lx and 8XC196Kx I/O ports.
5.2 INTERNAL STRUCTURE FOR PORTS 1, 2, 5, AND 6 (BIDIRECTIONAL
PORTS)
Figure 5-1 shows the logic for driving the output transistors, Q1 and Q2. Consult the datasheet
for specifications on the amount of current that each port can source or sink.
In I/O mode (selected by clearing a port mode register bit), the port data output and the port di-
rection registers are input to the multiplexers. These signals combine to drive the gates of Q1 and
Q2 so that the output is high, low, or high impedance.
In special-function mode (selected by setting a port mode register bit), SFDIR and SFDATA are
input to the multiplexers. These signals combine to drive the gates of Q1 and Q2 so that the output
is high, low, or high impedance. Special-function output signals clear SFDIR; special-function
Table 5-1. Microcontroller Ports
Port Pins Type
Configuration
Options
Associated Peripheral or
System Function
Port 0
8 (K x)
6 (CA, J x, Lx)
Standard Input-only
A/D converter
(not supported on LD)
Port 1
8 (K
x)
4 (CA, J x, Lx)
Standard
Complementary
Open-drain
EPA and timers
Port 2
8 (K x)
6 (CA, J x, Lx)
Standard
Complementary
Open-drain
J1850 (LB only), SIO,
interrupts, bus control, clock
gen.
Port 3 8 Memory mapped
Complementary
Open-drain
Address/data bus
Port 4 8 Memory mapped
Complementary
Open-drain
Address/data bus
Port 5
8 (K
x)
3 (CA, J x, Lx)
Memory mapped
Complementary
Open-drain
Bus control, slave port
Port 6
8 (K
x)
6 (CA, J x, Lx)
Standard
Complementary
Open-drain
EPA, SSIO