C505_9708 SIEMENS [Siemens Semiconductor Group], C505_9708 Datasheet - Page 71

• Manufacturer Part Number: C505_9708
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

6.1.3 Detailed Output Driver Circuitry
In fact, the pullups mentioned before and included in figure 6-2, 6-4 and 6-5 are pullup
arrangements. The differences of the port types available in the C505 are described in the next
sections.
6.1.3.1
Figure 6-6 shows the output driver circuit of the type B multifunctional digital I/O port lines. The
basic circuitry of these ports is shown in figure 6-4. The pullup arrangement of type B port lines has
one n-channel pulldown FET and three pullup FETs:
Figure 6-6
Driver Circuit of Type B Port Pins
Semiconductor Group
– The pulldown FET n1 is of n-channel type. It is a very strong driver transistor which is capable
– The pullup FET p1 is of p-channel type. It is activated for two oscillator periods (S1P1 and
– The pullup FET p2 is of p-channel type. It is always activated when a "1" is in the port latch,
Q
Input Data
(Read Pin)
of sinking high currents (
circuit to
the FET. This also means that no “0“ must be programmed into the latch of a pin that is used
as input.
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.
thus providing the logic high output level. This pullup FET sources a much lower current than
p1; therefore the pin may also be tied to ground, e.g. when used as input with logic low input
level.
Type B Port Driver Circuitry
V
=1
CC
must be avoided if the transistor is turned on, since the high current might destroy
Delay = 1 State
I
OL
); it is only activated if a "0" is programmed to the port pin. A short
<
_
=1
1
6-9
V
On-Chip Peripheral Components
SS
p1
n1
p2
=1
V
C505 / C505C
CC
p3
MCS03230
Port
Pin
1997-08-01