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User
’
s Manual
7-7
1999-08
7.3
Alternate Port Functions
In order to provide a maximum of flexibility for different applications and their specific IO
requirements, port lines have programmable alternate input or output functions
associated with them.
Table 7-1
Summary of Alternate Port Functions
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 effected by the alternate output function. The respective port latch should
hold a
‘
1
’
, because its output is combined with the alternate output data.
X-Peripherals (peripherals connected to the on-chip XBUS) control their associated IO
pins directly via separate control lines.
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, however,
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 purposes to allow a software trigger of an
alternate input function by writing to the port output latch.
Port
PORT0 Address and data lines when accessing
external resources (e.g. memory)
PORT1 Address lines when accessing external
resources (e.g. memory)
Port 2
Fast external interrupt inputs
Port 3
System clock or programmable frequ. output
Optional bus control signal
Input/output functions of timers,
serial interfaces
Alternate Function(s)
Alternate Signal(s)
AD15 ... AD0, D15 ... D0,
A15 ... A8
A15 ... A0
EX7IN ... EX0IN
CLKOUT/FOUT, BHE/WRH,
RxD0, TxD0, MTSR, MRST,
SCLK, T2IN, T3IN, T4IN,
T3EUD, T3OUT, CAPIN,
SDA0, SCL0
A22 ... A16
Port 4
Selected segment address lines in systems
with more than 64 KBytes of ext. resources
Analog input channels to the A/D converter
Timer control signal inputs
Chip select output signals
I
2
C interface lines
Port 5
AN3 ... AN0,
T2EUD, T4EUD
CS4 ... CS0,
SDA1, SCL1, SDA2
Port 6