Open Access
Circuit Descriptions
3-17
ARM Development Board (ARM7TDMI Version)
Hardware Reference Guide
ARM DUI 0017C
Note
When using the parallel port to connect to external devices, you are advised to remove all
the jumpers of link field (LK11). If you need to drive some LEDs and use an external device,
you should consider driving the LEDs connected to the PC card (PCMCIA) controller.
The ST16C552 can be configured through the use of two links:
• INT TYPE
• DIRN (LK8 and LK9)
LK8 selects the interrupt type, either latched mode (out) or ACK mode (in).
Latched mode A falling edge on the ACK pin is latched and causes a parallel
port interrupt. This interrupt is cleared by reading the
appropriate status register. Latched mode is the default.
ACK mode The ACK pin is connected directly to the parallel port interrupt
line. If the parallel port ACK line is not connected externally, it is
possible to make ACK pulse low by pressing the “momentary
action” switch, SW1 (which has a black cap). To enable this
function, the link ENABLE INT (LK10) must be inserted. If the
link is out, pressing the switch has no effect.
Note
When using the parallel port to connect to external devices, you are advised to remove the
jumper from ENABLE INT (LK10).
L9 (The DIRN link) is connected to the BIDEN pin on the ST16C552. You can program the
parallel port to be input or output under software control, but the method differs depending
upon the state of the BIDEN pin. The default is link out which means that BIDEN is high and
the direction is programmed by writing to the parallel port control register. Please refer to the
16C552 data sheet for further information.
Ref Name Description Options Default
LK8 INT TYPE latched or ACK mode out
in
=
=
latched
ACK
out
LK9 DIRN parallel port direction BIDEN select out
LK10 ENABLE INT enable switch interrupt out
in
=
=
disabled
enabled
out
Table 3-11: Link summary
hrg.book Page 17 Wednesday, July 22, 1998 9:18 AM
To Next Page
Loading...
