SAB80C517A-N18 Siemens Semiconductor Group, SAB80C517A-N18 Datasheet - Page 49

• Manufacturer Part Number: SAB80C517A-N18
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: Siemens Semiconductor Group

SAB 80C517A/83C517A-5
I/O Ports
The SAB 80C517A has seven 8-bit I/O ports and two input ports (8-bit and 4-bit wide).
Port 0 is an open-drain bidirectional I/O port, while ports 1 to 6 are quasi-bidirectional I/O ports
with internal pull-up resistors. That means, when configured as inputs, ports 1 to 6 will be
pulled high and will source current when externally pulled low. Port 0 will float when configured
as input.
Port 0 and port 2 can be used to expand the program and data memory externally. During an
access to external memory, port 0 emits the low-order address byte and reads/writes the data
byte, while port 2 emits the high-order address byte. In this function, port 0 is not an open-drain
port, but uses a strong internal pull-up FET. Port 1, 3, 4, 5 and port 6 provide several alternate
functions. Please see the "Pin Description" for details.
Port pins show the information written to the port latches, when used as general purpose port.
When an alternate function is used, the port pin is controlled by the respective peripheral unit.
Therefore the port latch must contain a "one" for that function to operate. The same applies
when the port pins are used as inputs. Ports 1, 3, 4 and 5 are bit- addressable.
The SAB 80C517A has two dual-purpose input ports. The twelve port lines at port 7 and port
8 can be used as analog inputs for the A/D converter. If input voltages at P7 and P8 meet the
specified digital input levels (V
) the port can also be used as digital input port.
V
IL and
IH
In Hardware Power Down Mode the port pins and several control lines enter a floating state.
For more details see the section about Hardware Power Down Mode.
Semiconductor Group
48
1994-05-01