User’s Manual
6-13
05.99
On-Chip Peripheral Components
C513AO
6.1.5 Port Loading and Interfacing
The output buffers of Ports 2 and 3 can drive TTL inputs directly. Refer to the DC characteristics in
the Data Sheet of the C513AO for the maximum port load which still guarantees correct logic output
levels. The corresponding parameters are
V
OL
and
V
OH
.
The output buffers of Port 0 can also drive TTL inputs directly. They do, however, require external
pull-ups to drive floating inputs, except when used as the address/data bus.
It must be noted that when used as inputs, Ports 2 and 3 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 is
applied to the port pin (Parameters
I
TL
and
I
IL
in the DC Characteristics of the C513AO Data Sheet
specify these currents). Port 0 has floating inputs when used for digital input.
