Rabbit Rabbit 4000, User Manual

Page: 111 / 358

Chapter 12 Parallel Port E 101
12.2.3 Other Registers
12.2.4 Interrupts
External interrupts can be accepted from pins PE5, PE4, PE1 or PE0; see Chapter 7 for
more details.
12.3 Operation
The following steps must be taken before using Parallel Port E.
1. Select the desired input/output direction for each pin via PEDDR.
2. Select high/low or open-drain functionality for outputs via PEDCR.
3. If an alternative peripheral output function is desired for a pin, select it by via PEALR
or PEAHR and then enable it via PEFR. Refer to the appropriate peripheral chapter for
further use of that pin.
Once the port is set up, data can be read or written by accessing PEDR. The value of an
output pin read in from PEDR will reflect its current output value, but any value written to
an input pin will not appear until that pin becomes an output.
Register Function
SACR, SBCR, SCCR,
SDCR, SECR, SFCR Select a Parallel Port E pin as serial data (and
optional clock) input.
ICS1R, ICS2R
Select a Parallel Port E pin as a start/stop condition
input.
QDCR Select a Parallel Port E pin as a decoder input.
I0CR, I1CR
Select a Parallel Port E pin as an external interrupt
input.
DMR0CR, DMR1CR
Select a Parallel Port E pin as an external DMA
request input.
NACR Select PE6 as the Ethernet clock input.
SPCR Select slave chip select on PE7.
IHSR, IHTR