ST10R272L - PARALLEL PORTS
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Each port line has one programmable alternate input or output function associated with
it. PORT0 and PORT1 may be used as the address and data lines when accessing
external memory.
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Port 2 is used for fast external interrupt inputs.
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Port 3 includes alternate input/output functions of timers, serial interface, the optional
bus control signal BHE and the system clock output (CLKOUT).
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Port 4 outputs the additional segment address bits A23/19/17...A16 in systems where
more than 64 KBytes of memory are to be accessed directly.
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Port 5 is used for timer control signals.
Port 6 provides the optional chip select outputs and the bus arbitration lines.
Alternate input or output function of port
If an alternate output function of a pin is to be used, the direction of this pin must be
programmed for output (DPx.y=‘1’), except for some signals that are used directly after reset
and are configured automatically. Otherwise the pin remains in the high-impedance state
and is not affected by the alternate output function. The respective port latch should hold a
‘1’, because its output is ANDed with the alternate output data.
If an alternate input function of a pin is used, the direction of the pin must be programmed for
input (DPx.y=‘0’) if an external device is driving the pin. The input direction is the default after
reset. If no external device is connected to the pin, one can also set the direction for this pin
to output. In this case, the pin reflects the state of the port output latch. Thus, the alternate
input function reads the value stored in the port output latch. This can be used for testing
Figure 26 Output drivers in push/pull and open drain mode