This simple design using the Nascom PIO lets the
microcomputer do all the work and reduces the hardware
requirements to 2 4040 CMOS counter, a few small components, a
piece of Veroboard and a 25 volt power supply. It gives you a
‘user-friendly’, almost foolproof design for just under 1K of
object code which can either be stored on tape and operated from
RAM or itself programmed into an EPROM for use. The software is
written for Nas-Sys 1 and will run on a Nascom 2 or expanded
The program sets the ports to mode 3, initiates the outputs,
checks the 5 volt supply and reminds you to switch on but not
insert the EPROM yet.
It asks whether a 2716
is to be programmed, reminds
you to set the type switch and checks that it is in the correct
It then tells you to switch off, insert the EPROM and switch
on again and, after checking that the supply has been cut and
restored, finally displays the menu of options, and of which may
be selected. These are :–
Check EPROM completely erased.
Dump to RAM for examination.
Program and check against source.
Return to monitor.
Options 2 and 4 allow use of the normal tabulate function to
find unused sections of the EPROM and option 3 programs as many
bytes as required from any address in memory to any part of the
When the RAM source address, EPROM start address and number
of bytes have been entered, a prompt for a final start command
is given to allow time to cross-check before committing the
EPROM to programming.
During the latter, a pair of rapidly changing symbols is
displayed to avoid the impression that nothing is happening.
When both symbols are null characters, the programming is
complete and the EPROM is checked against its RAM source and a
correct or error message displayed before the program returns to
Port A is used to write data to or read it from the EPROM
and Port B uses four bits as outputs to control the 4040 address
counter, the programming logic and the voltage switch, and two
bits as inputs to check the switch positions. The latter may