80-Bus News


July–August 1984, Volume 3, Issue 4

Page 18 of 43


START QU FOL5H sStart of code after sthe jump table in SIMON 1 F000 C313F3 JP PAGEON :Changed jump to select Page 1 F313 F5 PAGEON: PUSH AF sSave A and Flags F314 3E11 LD A, 11H s;Load System Page No.(0) in A F316 D3FF OUT (FFH),A sSelect Page 0 F318 Fl POP AF ;Recover A and Flags F319 C315F0 JP START ;Go boot CP/M END


There are other ways to do it, but the above code works on both of my Nascoms, and CP/M, CCPZ etc, boot up and run with either GM862 or GM802 RAM boards installed. Having got thus far, there was still the job of configuring CP/M to actually drive the other memory page/s as RAMDISK. If Gemini’s CONFIG.COM is available for the version of CP/M used, then it’s a doddle. One simply selects Menu option 8 (7 on some versions) and if you are using the GM862, have SIMON in EPROM at F000h, and run 60K CP/M or whatever, enter 3 for the number of extra pages and 60 for the Kilobyte size of each page. By selecting the appropriate number of pages, CONFIG can accommodate up to three additional 64K GM802 boards in the same manner, but do NOT specify more boards or pages of RAM than are installed because the system will crash and/or fail to boot. Test the system by typing M: to select the RAMDISK, when the M> or MO> prompt should appear. A DIR command should respond with a NO FILE message. Return to *normal’ via an A: command and type STAT M: when the response should indicate between 172K and 178K “bytes free” if three 60K pages are in use. If only one 60K page is in use the response will be a (disappointing) 52K to 58K depending upon the size of the BIOS and the allocated RAMDISK Directory. Try PIPing and STATing programs around between Disk and RAM to ensure that all is well. SWEEP may also be used, but the versions written in high level code hang-up if zero sized files are transmitted and exhibit a few other minor bugs. However NSWEEP 2.07, a later Z80 code version, has behaved faultlessly with RAMDISKs. The proven configuration on the Disk system tracks may now be SYSGENed onto other disks or the configuration process can be repeated as required.


To activate Page mode RAMDISK operation under later versions of SYS requires that module SYSB1 be re-assembled using M80 with the appropriate software switches set as follows:–

vdisk equ true sVirtual disk i.e. RAMDISK support

vboot equ true(or false) ;Boot from virtual disk (best set to sfalse at first, but recommended)

vdrive equ 12(or15) ;Drive letter (12=M,15=P) as preferred

vflip equ false ;Else on own your head be it!

vgem equ true ;Set map32, map4 and g833 false

vbmem equ 60 360K when SIMON is in EPROM at F000H

vnum equ 2(1,0r3) s;Number of boards/pages see * below

smay be 3 only if SYS is modified vnom equ 1(or2) ;System page, normally 0 (1=Pg0)

This is an OCR’d version of the scanned page and likely contains recognition errors.

Page 18 of 43