SAB-C509-LM SIEMENS [Siemens Semiconductor Group], SAB-C509-LM Datasheet - Page 40

• Manufacturer Part Number: SAB-C509-LM
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

C509-L
Port Structure Selection
After a reset operation of the C509-L, the quasi-bidirectional 8051-compatible port structure is
selected. For selection of the bidirectional port structure (CMOS) the bit PMOD of SFR SYSCON
must be set. Because each port pin can be programmed as an input or an output, additionally, after
the selection of the bidirectional mode the direction register of the ports must be written (except the
analog/digital input ports 7,8). This direction registers are mapped to the port registers. This means,
the port register address is equal to its direction register address. Figure 16 illustrates the port- and
direction register configuration.
Figure 16
Port Register, Direction Register
For the access the direction registers a double instruction sequence must be executed. The first
instruction has to set bit PDIR in SFR IP1. Thereafter, a second instruction can read or write the
direction registers. PDIR will automatically be cleared after the second machine cycle (S2P2) after
having been set. For this time, the access to the direction register is enabled and the register can
be read or written. Further, the double instruction sequence as shown in figure 16, cannot be
interrupted by an interrupt,
When the bidirectional port structure is activated (bit PMOD in SFR SYSCON =1) after a reset, the
ports are defined as inputs (direction registers default values after reset are set to FF H ).
With PMOD = 0 (quasi-bidirectional port structure selected), any access to the direction registers
has no effect on the port driver circuitries.
Semiconductor Group
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