Rainbow Electronics AT91CAP9S250A - Manual (Page 35)

35
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
10.3 Peripherals Signals Multiplexing on I/O Lines
The AT91CAP9S500A/AT91CAP9S250A features 4 PIO controllers, PIOA, PIOB, PIOC and
PIOD, that multiplex the I/O lines of the peripheral set.
Each PIO Controller controls up to 32 lines. Each line can be assigned to one of two peripheral
functions, A or B. The multiplexing tables in the following paragraphs define how the I/O lines of
the peripherals A and B are multiplexed on the PIO Controllers. The two columns “Function” and
“Comments” have been inserted in this table for the user’s own comments; they may be used to
track how pins are defined in an application.
Note that some peripheral functions which are output only may be duplicated within both tables.
The column “Reset State” indicates whether the PIO Line resets in I/O mode or in peripheral
mode. If I/O is mentioned, the PIO Line resets in input with the pull-up enabled, so that the
device is maintained in a static state as soon as the reset is released. As a result, the bit corre-
sponding to the PIO Line in the register PIO_PSR (Peripheral Status Register) resets low.
If a signal name is mentioned in the “Reset State” column, the PIO Line is assigned to this func-
tion and the corresponding bit in PIO_PSR resets high. This is the case of pins controlling
memories, in particular the address lines, which require the pin to be driven as soon as the reset
is released. Note that the pull-up resistor is also enabled in this case.