User’s Manual
6-3
05.99
On-Chip Peripheral Components
C513AO
Figure 6-3
Output Driver Circuit of Ports 1, 2 and 3 (except P1.2, P1.3, P1.4 and P1.5)
One n-channel pull-down FET and three pull-up FETs are used in the example shown in Figure 6-3.
– The pull-down FET n1 is of n-channel type. It is a very strong transistor which is capable of
sinking high currents (
I
OL
); it is only activated if a “0” is programmed to the port pin. A short
circuit to
V
DD
must be avoided if the transistor is turned on, since the high current might destroy
the FET. This also means that no “0” must be programmed into the latch of a pin that is used
as input.
– The pull-up FET p1 is of p-channel type. It is activated for one state (S1) if a 0-to-1 transition
is programmed to the port pin; that is, a “1” is programmed to the port latch which contained
a “0”. The extra pull-up can drive a current similar to the pull-down FET n1. This provides a
fast transition of the logic levels at the pin.
– The pull-up FET p2 is of p-channel type. It is always activated when a “1” is in the port latch,
thus providing the logic high output level. This pull-up FET sources a much lower current than
p1. Therefore, the pin may also be tied to the ground; for example, when used as input with
logic low input level.
– The pull-up FET p3 is of p-channel type. It is activated only if the voltage at the port pin is
higher than approximately 1.0 to 1.5 V. This provides an additional pull-up current if a logic
high level shall be output at the pin (and the voltage is not forced lower than approximately
1.0 to 1.5 V). However, this transistor is turned off if the pin is driven to a logic low level; that
is, when used as input. In this configuration, only the weak pull-up FET p2 is active, which
sources the current
I
IL
. If, in addition, the pull-up FET p3 is activated, a higher current can be
sourced
(I
TL
). Thus, an additional power consumption can be avoided if port pins are used as
inputs with a low level applied. However, the driving capability is stronger if a logic high level
is output.
MCS01824
= 1
1
= 1
= 1
V
DD
Port
Pin
SS
V
Q
Input Data
(read pin)
p1
p2
p3
n1
2 Osc. Periodes
Delay =
_
<