C509-L_97 Datasheet, PDF (79/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

On-Chip Peripheral Components
C509-L
6
On-Chip Peripheral Components
This chapter gives detailed information about all on-chip peripherals of the C509-L except for the
integrated interrupt controller, which is described separately in chapter 7.
6.1
Parallel I/O
6.1.1 Port Structures
Digital I/O Ports
The C509-L allows for digital I/O on 64 lines grouped into 8 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 P6 and P9 are performed via their corresponding special function registers P0 to P6 and
P9. The port structure of the C509-L is designed to operate either as a quasi-bidirectional port
structure, compatible to the standard 8051-Family, or as a genuine bidirectional port structure. This
port operating mode can be selected by software (setting or clearing the bit PMOD in the SFR
SYSCON).
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 7 and 8 are available as input ports only and provide for two functions. When used as digital
inputs, the corresponding SFR’s P7 and P8 contain the digital value applied to port 7 and port 8
lines. When used for analog inputs the desired analog channel is selected by a three-bit field in SFR
ADCON0 or a four-bit field in SFR ADCON1. Of course, it makes no sense to output a value to these
input-only ports by writing to the SFR’s P7 or P8; 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 P7 and P8 are not bit-addressable registers, all input lines of P7 or P8 are read at
the same time by byte instructions.
Nevertheless, it is possible to use ports 7 and 8 simultaneously for analog and digital input.
However, care must be taken that all bits of P7 or P8 that have an undetermined value caused by
their analog function are masked.
In order to guarantee a high-quality A/D conversion, digital input lines of port 7 and port 8 should
not toggle while a neighboring port pin is executing an A/D conversion. This could produce crosstalk
to the analog signal.
Semiconductor Group
6-1
1997-10-01