SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 39

• Manufacturer Part Number: SAB80C517-M16
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

7
This chapter gives detailed information about all on-chip peripherals of the SAB 80C517 except for
the integrated interrupt controller, which is described separately in chapter 8. Sections 7.1 and 7.2
are associated with the general parallel and serial I/O facilities while the remaining sections
describe the miscellaneous functions such as the timers, A/D converter, compare/capture unit,
multiplication/division unit, power saving modes, "fail-save" mechanisms, oscillator and clock
circuitries and system clock output.
7.1
7.1.1
Digital I/O
The SAB 80C517 allows for digital I/O on 56 lines grouped into 7 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 are performed via their corresponding special function registers P0 to P6.
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 (see also chapter 7.1.2 and chapter 5 for more details about the external bus interface).
Digital/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, as described in section 7.4. 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
(
the same time by byte instructions.
Semiconductor Group
V
IL
/
V
IH
). Since P7 and P8 are not bit-addressable registers, all input lines of P7 or P8 are read at
On-Chip Peripheral Components
Parallel I/O
Port Structures
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On-Chip Peripheral Components