When installing the Nascoa F.0.C. card or any asseably using
an off-board P.1.0. on a Nascom i, you will find that the
on-board P.1.0. will no longer function. This is because the
decoding for selecting ports 0 to 3 (keyboard and UART) from
ports 4 to 7 (P.1,0.) relied on the I/O select link being wired
to TINT? which is actually a2.
Once the I/O select 15 moved to “EXT”, which is actually
NasI0, the address line a2 is disconnected and the port decoding
As incomplete, causing any reference to ports 4 to 7 to be
directed to ports 0 to 3 respectively.
If the P.1.0. was in use prior to the addition of discs then
the only advice that Nascom can offer is that you buy a P.T.0.
board, not a very economic method of sorting out this simple
problem. There follows a method that will solve the port
decoding problem for approx. 20p plus labour.
1x 74LS02 Quad NOR Gate
3% lengths of wire 30cm Long
Nascom 1 circuit sheet 1
1. Locate IC 48 (7aLS00)
2. Remove, bend out pin 2, replace.
3. Take 74LS02, bend sideways all pins except pins 1,741)
41 Solder 74/502 on top of 74L500 using pins 7 and 14.
5. Bend pin 1 of 74L502 to join pin 2 of 74LSO0.
6. Solder these two pins.
7. Remove link on I/O select completely.
@. Connections to 741502 are as follows:
pin 10 to pin 11
pin Ztopin 4
pin 2 to pin 8 to I/O select ‘ExT’
pin Stopin 9 to I/O select “INT?
pin 13 to I/O select ‘COM’
Ground from pin 7 to pin & and pin 12
Once the wiring changes have been made, all that needs to be
done is to reassemble and test.
Using the NAS-SYS commands ‘O’ and ‘O”, type the following:
1.06 OF Initialise port A as an output.
2:0 7 OF Initialise port B as an output.
5.04.55 Send SSH to port A.
This is an OCR’d version of the scanned page and likely contains recognition errors.