C515 Datasheet, PDF (24/55 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C515
Digital I/O Ports
The C515 allows for digital I/O on 48 lines grouped into 6 bidirectional 8-bit ports. Each port bit
consists of a latch, an output driver and an input buffer. Read and write accesses to the I/O ports P0
through P5 are performed via their corresponding special function registers P0 to P5.
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.
Analog Input Ports
Ports 6 is available as input port only and provides two functions. When used as digital inputs, the
corresponding SFR P6 contains the digital value applied to the port 6 lines. When used for analog
inputs the desired analog channel is selected by a three-bit field in SFR ADCON. Of course, it
makes no sense to output a value to these input-only ports by writing to the SFR P6. This will have
no effect.
lf a digital value is to be read, the voltage levels are to be held within the input voltage specifications
(V_IL/V_IH). Since P6 is not bit-addressable, all input lines of P6 are read at the same time by byte
instructions.
Nevertheless, it is possible to use port 6 simultaneously for analog and digital input. However, care
must be taken that all bits of P6 that have an undetermined value caused by their analog function
are masked.
Semiconductor Group
24
1997-08-01