C508_01 Datasheet, PDF (79/267 Pages) Infineon Technologies AG – 8-Bit CMOS Microcontroller

C508
On-Chip Peripheral Components
6.1.5 Port Loading and Interfacing
The output buffers of Ports 1 to 5, except Port 4 can drive TTL inputs directly. The
maximum port load which still guarantees correct logic output levels can be looked up in
the DC characteristics in the Data Sheet of the C508. The corresponding parameters are
V_OL and V_OH.
The same applies to Port 0 output buffers. They do, however, require external pull-ups
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 5 (except Port 4) are not floating
but have internal pull-up 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_TL
and I_IL in the DC characteristics specify these currents). Port 0 however, has floating
inputs when used for digital input.
User’s Manual
6-14
2001-05