SAB80C517-M16 SIEMENS [Siemens Semiconductor Group], SAB80C517-M16 Datasheet - Page 40

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

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 neighbouring port pin is executing an A/D conversion. This could produce
crosstalk to the analog signal.
Digital I/O Port Circuitry
Figure 7-1 shows a functional diagram of a typical bit latch and I/O buffer, which is the core of each
of the 7 I/O-ports. The bit latch (one bit in the port’s SFR) is represented as a type-D flip-flop, which
will clock in a value from the internal bus in response to a "write-to-latch" signal from the CPU. The
Q output of the flip-flop is placed on the internal bus in response to a "read-latch" signal from the
CPU. The level of the port pin self is placed on the internal bus in response to a "read-pin" signal
from the CPU. Some instructions that read from a port (i.e. from the corresponding port SFR P0 to
P6) activate the "read-latch" signal, while others activate the "read-pin" signal (see section 7.1.4.3).
Figure 7-1
Basic Structure of a Port Circuitry
Semiconductor Group
Int. Bus
Read
Latch
Latch
Read
Write
to
Pin
D
CLK
Port
Latch
41
Q
Q
On-Chip Peripheral Components
Port
Driver
Circuit
MCS01822
Port
Pin