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C509-L Datasheet(PDF) 40 Page - Siemens Semiconductor Group |
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C509-L Datasheet(HTML) 40 Page - Siemens Semiconductor Group |
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40 / 74 page  Semiconductor Group 39 09.96 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 FFH). With PMOD = 0 (quasi-bidirectional port structure selected), any access to the direction registers has no effect on the port driver circuitries. |
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