Nascom 1 & 2 Graphics ROM Editor

by Z.A. Lesiakowski

For those of you with an EPROM blower wanting to create your own set of characters, the accompanying program will allow you to easily create, change and amend each character cell. It is written in machine code and will run under Nas-Sys.

As most of you are already aware, each character cell for the N1 is made up of 16 rows of 8 dots whereas for the N2 it is 14 rows of 8 dots, the last two rows being unused by the N2. As there are 128 characters in a character EPROM, the EPROM must be 16 x 128 bytes, ie. 2K. On executing the program you will be asked whether you are programming an N1 or N2 EPROM followed by the origin of the 2K of RAM where the characters will be stored. Characters are produced by using the commands listed below and storing them an tape ready for blowing into EPROM. (NB the origin must be above 1700H)

Commands.

CTRL/F –

will Fill the character RAM area with FFH. Thus, unprogrammed locations will remain at FFH enabling you to overprogram the characters at a later date.

I –

will Increment the location number displayed in the corner of the screen. This number corresponds to the alphanumeric address given in your Nascom manual. For the Graphics characters simply add 80H to the location number.

D –

will Decrement the location number.

G –

will Get a character from RAM specified by the location number and place it into the character cell.

C –

will Complement a character within the cell.

B –

will Blank or clear the character cell.

R –

will Reflect a character in the cell. This is very useful when two characters are used to produce a symetrical shape such as a pawn from a chess set.

S –

will Save the character from the character cell into the specified RAM location number.

V –

will Invert a character in the cell.

u –

will roll the character in the cell up.

d –

will roll the character in the cell down.

l –

will roll the character in the cell left.

r –

will roll the character in the cell right.