C515C_9711 Datasheet, PDF (75/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C515C
6.1.1.3 Bidirectional (CMOS) Port Structure of Port 5
Port 5 of the C515C provides a special port structure: This port is designed to operate either as a
quasi-bidirectional port structure, compatible to the standard 8051-Family, or as a genuine
bidirectional port structure with CMOS level driving capabilities. This bidirectional CMOS port
operating mode can be selected by software by setting or clearing bit PMOD in SFR SYSCON (see
chapter 6.1.1.1). After reset the quasi-bidirectional port structure is selected.
Based on the port structure of a port circuitry as shown in figure 6-1, the following sections describe
the different operating modes (input mode, output mode, hardware power-down mode) of port 5.
6.1.1.3.1 Input Mode
Figure 6-9 shows the bidirectional port structure in the input mode.
V_CC
QDL
PMOD
HWPD
"1" _&
"1"
"1" ^{= 1}
Input Data
(read pin)
"1"
1
p1 ^"1"
p2 ^"1"
= 1 _"0"
n1
1
V_SS
CMOS
&
=1
p3
Port
Pin
p5
n2
QDL : Direction Latch, Output Q
V_SS
MCS02650
Figure 6-9
Bidirectional Port Structure - Input Mode
The input mode for a port 5 pin is selected by programming the corresponding direction bit to '1'
(QDL='1'). The FETs p1, p2, p3 and n1 are switched off. Through a Schmitt-Trigger, designed to
detect CMOS levels, the input signal is lead to the internal bus where it can be read by the
microcontroller.
Semiconductor Group
6-12
1997-11-01