SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 41

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Port 1 through 6 output drivers have internal pullup FET’s (see figure 7-2). Each I/O line can be
used independently as an input or output. To be used as an input, the port bit must contain a one
(1) (that means for figure 7-2: Q = 0), which turns off the output driver FET n1. Then, for ports 1
through 6, the pin is pulled high by the internal pullups, but can be pulled low by an external source.
When externally pulled low the port pins source current (
sometimes called "quasi-bidirectional".
Figure 7-2
Basic Output Driver Circuit of Ports 1 through 6
In fact, the pullups mentioned before and included in figure 7-2 are pullup arrangements as shown
in figure 7-3. One n-channel pulldown FET and three pullup FETs are used:
Semiconductor Group
– The pulldown FET n1 is of n-channel type. lt is a very strong driver transistor which is capable
– The pullup FET p1 is of p-channel type. lt is activated for two oscillator periods (S1P1 and
of sinking high currents (
circuit to
the FET.
S1P2) if a 0-to-1 transition is programmed to the port pin, i.e. a "1" is programmed to the port
latch which contained a "0". The extra pullup can drive a similar current as the pulldown
FET n1. This provides a fast transition of the logic levels at the pin.
V
CC
must be avoided if the transistor is turned on, since the high current might destroy
Int. Bus
Read
Latch
Latch
Read
Write
to
Pin
I
OL
); it is only activated if a "0" is programmed to the port pin. A short
D
CLK
Bit
Latch
42
On-Chip Peripheral Components
Q
Q
I
IL
or
MCS01823
I
TL
V
). For this reason these ports are
CC
n1
Internal
Pull Up
Arrangement
Pin