C505_9708 SIEMENS [Siemens Semiconductor Group], C505_9708 Datasheet - Page 75

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

On-Chip Peripheral Components
C505 / C505C
6.1.5 Port Loading and Interfacing
The output buffers of ports 1 to 4 can drive TTL inputs directly. The maximum port load which still
guarantees correct logic output levels can be be looked up in the DC characteristics in the Data
Sheet of the C505 or in chapter 10 of this User’s Manual. The corresponding parameters are
V
OL
V
and
.
OH
The same applies to port 0 output buffers. They do, however, require external pullups to drive
floating inputs, except when being used as the address/data bus.
When used as inputs it must be noted that the ports 1 to 4 are not floating but have internal pullup
transistors. The driving devices must be capable of sinking a sufficient current if a logic low level
shall be applied to the port pin (the parameters
I
and
I
in the DC characteristics specify these
TL
IL
currents). Port 0 as well as port 1 programmed to analog input function, however, have floating
inputs when used for digital input.
Semiconductor Group
6-13
1997-08-01