From: cbmvax.cbm!fred (Fred Bowen)
Subject: 1541B ROM update
Date: 12 Dec 86 23:14:51 GMT
To: Commodore users


1541B DOS ROM RELEASE NOTES
Commodore Electronics, LTD.                     5 December 1986

1541B ROM RELEASE NOTES: 251968-02   (16K byte, 300ns, checksum=$1A69)

THE FOLLOWING MODIFICATIONS HAVE BEEN MADE TO THE  251968-01  ROM  CODE  TO
CREATE A NEW ROM  RELEASED  ON  12/05/86.  THIS  RELEASE IS MADE TO  CREATE
MASKED ROMS FOR PRODUCTION OF THE 1541B/C MODEL DISK DRIVE ONLY.

1.  The interrupt rate change from 15 to 8ms for slightly better
performance caused compatibility problems with some software that used that
timing for its own purposes. It is now 15ms.

2.  The 1541B  board  has  troubles  accessing tracks beyond 35
attributable to the new data separator, although the problem always existed
(wrong bit cell densities because TRKNUM only listed up to track 35).
TRKNUM has been extended.

3.  SAVE-@ (SAVE with replace) is fixed.  The variable  NODRV is now a
16-bit addressable var,  and the STLBUF routine steals the buffer locked by
drive one.

4.  Relative File fixes (unspecified).

5.  Serial bus (DEVICE NOT PRESENT) fix.  TSTATN now clears IRQ.

6.  Block read fix (unspecified).

7.  Write to stack area bug (unspecified).

8.  Set decimal mode (SED) before disabling IRQ (SEI) fixed.

9.  Disk full bug (unspecified).

10.  Add copyright notice for legal types and thieves.

11.  The ROM checksum adjustment byte at $C001 is now $46.

 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  PLEASE NOTE:  THIS ROM WILL _NOT_ WORK IN EARLIER 1541 PCB'S, WHICH
REQUIRE DIFFERENT SIZED ROMS (8K),  AMONG OTHER BOARD DIFFERENCES!
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
-- 
Fred Bowen

Commodore Electronics, Ltd.,  1200 Wilson Drive,  West Chester,  PA,  19380