C541U_99 Datasheet, PDF (46/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
6 On-Chip Peripheral Components
This chapter gives detailed information about all on-chip peripherals of the C541U except for the
integrated interrupt controller, which is described separately in chapter 7.
6.1 Parallel I/O
The C541U three 8-bit I/O ports and one 6-bit I/O port (Port 1). Port 0 is an open-drain bidirectional
I/O port, while ports 1 to 3 are quasi-bidirectional I/O ports with internal pullup resistors. That means,
when configured as inputs, ports 1 to 3 will be pulled high and will source current when externally
pulled low. Port 0 will float when configured as input.
The output drivers of port 0 and 2 and the input buffers of port 0 are also used for accessing external
memory. In this application, port 0 outputs the low byte of the external memory address, time
multiplexed with the byte being written or read. Port 2 outputs the high byte of the external memory
address when the address is 16 bits wide. Otherwise, the port 2 pins continue emitting the P2 SFR
contents. In this function, port 0 is not an open-drain port, but uses a strong internal pullup FET.
Two port lines of port 1 (P1.0/LED0, P1.1/LED1) and one port line of port 3 (P3.0/LED2) have the
capability of driving external LEDs in the output low state.
Semiconductor Group
6-1
1999-04-01