Nascom News­let­ter

ZEAP. If in doubt use Y in ZEAP but it should not be necessary. zzzz is 2000H for tape or disc ZEAP and 1000H for my EPROM version. xxyy is the length of the buffer found at 3B00 (yy) and 3B01 (xx) and is always found in the first two bytes of ZEAP buffers. Adding the length to the start of the buffer produces a location after an FF (stop byte). Of course the pseudo ops do not all translate and in both types of file I keep hex references with leading 0’s and trailing H’s. Don’t drop ’en – your H’s that is.

Meanwhile, back in NAS-ASS – one bother is removing lines with shift and cursor because empty lines are not entered with the enter key. This may not be obvious till assembly or re-entry to text edit mode. Use CTRL K to be sure. I usually spray edit commands all over the text and then struggle to recall why I used the LDIR mnemonic. What cruel set of circumstances conspired to create this as an editor directive?

The put instruction does not cope if the last line of the inserting code is consequitive with the insertion line.

In the manual LSB and MSB pseudo ops are the LSB (Least Significant Boob). The op itself actually inserts one code byte into the program, what a strange device!

If, like me, you wish to assign any variable with one byte for INT vectors then the LET will let (ha) you – eventually.

LET

LOBYTE=INTLAB & 0FFH       ;easy

LET

HIBYTE=((INTLAB & 0FF00H)/256) & 0FFH   ;phew

Points to remember are that division rounds off after and puts F’s in the high byte hence the & 0FFH

Now, let me fill you in the rest of the Editor (not you Ed).

ASCII & MAP – remind you of codes for keys and display – nice touch that.

Construct – pulls raw data from memory and enters it as DEFB or DEFW – very useful.

D & H – allows decimal to hex and back to be worked out before committing to text. Both these are useful and better than one alone.

ZTC/​CTZ – converts to and from ZEAP format (with caution).
EDIT – text edit mode is screen based, mostly cursor controlled. Lines are not numbered on screen like ZEAP but one line number is displayed for the cursor position. Mixed views here.

Find instructions do work well and can be repeated.

Block move commands do well (with one reservation).

/ – loads and executes any file in editor. Some commands (but not all those you would expect) are repeated in the assembler which is an overlay from disc.