Hello Malisa!

I'm sorry to hear that you are having problems with the circuit, and hope
that you will be able to correct them with the info I now send you.

My original LaceScan archives do not contain a full description of the
connections to be made (and cut) in the computer, since there are so
many models and PCB revisions.  A complete guide to these would be HUGE!

From your description it sounds as if you have already found the correct
points to connect the new (and cut the old) Display-Enable signals.
You do not mention the autoswitch control signal at all however,
from which I draw the conclusion that this signal is the problem.

The signal needed is pin 5 of the ACIA (MC6850) that communicates with
the keyboard.  Unfortunately that pin is erroneously connected to the
corresponding output of the other ACIA, which handles MIDI ports.
These pins represent the RTS (Ready-To-Send) signals of the ACIA's, but
are never used, and indeed cannot be used due to the error mentioned.

This is a fault in MEGA ST design, which I have not seen in STFMs.
On the STFMs I have seen these pins are, correctly, not connected.

It is necessary to disconnect these pins from each other, and then connect
pin 5 of the keyboard-ACIA to the data input of the main autoswitch latch.
(Via the switch S1, so it can be physically disabled. See AUTOLACE.IMG)

This reconnection can be achieved by several methods,
listed below in order of preference:

  1:	If your ACIA's are mounted in sockets, simply remove keyboard-ACIA
	and carefully straighten pin 5 with pliers.  Then replace the ACIA
	in its socket, making sure that pin 5 does not touch any metal.
	Finally solder a lead from your autoswitch circuit to ACIA pin 5.

  2:	Trace the PCB circuits connecting pins 5 of both ACIAs, and look
	for a suitable place to cut the connection. Cut it very carefully!
	Scrape the green laquer off the trace leading to keyboard ACIA pin 5.
	Finally solder a lead from your autoswitch circuit to the PCB trace.

  3:	If you dislike cutting PCB traces you can instead desolder pin 5 of
	the keyboard-ACIA and carefully bend it up from the PCB.
	Be careful not to break the pin where it enters the IC body, since
	that will make reconnection impossible.  Once pin 5 is free, solder
	a lead from your autoswitch circuit to it.
	This method requires a good desoldering gun and bent-nose pliers !!!

  4:	As a variant of method 3, you can simply cut pin 5 at the point where
	it is soldered to the PCB and carefully bend the remainder up so it
	touches no metal, and then proceed as above.

Once these changes have been made it should be possible to switch between
normal and overscan mode under software control, either by using the 'hotkey'
commands of LaceScan, or by using the utility programs:

  LACE_1.PRG	switches keyboard ACIA pin 5 high to enable overscan
  LACE_0.PRG	switches keyboard ACIA pin 5 low to disable overscan
  
"LACE_1.PRG" should precede "LACESCAN.PRG" in the auto folder when booting
if you want LaceScan to activate overscan mode directly on starting.

The sync problem you also mention is not surprising, since the latch which
passes the autoswitch signal to the NAND gates is also responsible for
ensuring that this happens with the correct timing.  Even so, there is
a problem with some shifter chips that causes them sometimes to start up
out of sync, but a new hardware reset of the computer usually fixes this.

I hope this will solve your problems with the autoswitch hardware, and to make
sure that your software is up to date I enclose a diskette with LaceScan 3.1,
which is the current version.

In the newer versions I have added an optional emulator program (LACE_EMU.PRG),
which is not needed to use the basic overscan modes or the standard ST modes.
This emulator is similar to "MonSTEr" and "Big_Scrn", except that it has more
emulation modes and can use overscan modes for a larger physical display.
When used, it consumes appx 200 Kbyte of RAM to emulate a large variety of
resolutions including TT-medium (colour monitor) and TT-high (any monitor).

If you have any further problems and/or other feedback concerning LaceScan,
please feel free to write me again.

Cordially:
		Ulf Ronald Andersson
		H”ders V„g 7
		S-14570 Norsborg
		Sweden

P.S:	I hope the diskette arrives in readable condition,
	but if not simply send it back so we can try again.
D.S.
