SID/ZSID/DDT Console Redirection Patch

	SID2TTY is a small, public-domain program that
dynamically patches the SID debugger (Data Resources, Inc.) to
redirect all of SID's console input and output to the logical TTY:
device.  (ZSID2TTY and DDT2TTY are the ZSID and DDT versions.)

By using a second terminal as the TTY: device to "command" SID,
one can debug programs without interfering with standard console
input and output.  Thus, (assuming the usual CON:=CRT:
assignment) a program's standard output will appear on the video
monitor exactly as if the debugger were not in use, and program
input will be entered on the standard keyboard.

The patch itself is just 23 bytes -- it changes the IOBYTE each time
SID calls for bdos console i/o service and restores it afterwards. 
The patch is relocated to protected high memory, below SID (and
below any .SYM and .UTL files, which should be loaded first).

Source file:	SID2TTY.ASM for assembly with ASM or MAC.
		The ZSID and DDT versions are obtained by
		changing three equates.

Requirements:	CP/M 2.2 - 3.0 with IOBYTE implemented in bios.
		8080, 8085 or Z80 CPU.
		SID v. 1.4 or ZSID v. 1.4 or DDT v2.2.
		External terminal connected to TTY:

Installation:	Set the equates for SID, ZSID or DDT.
		If your TTY: device needs initialization or
		de-initialization, insert the code in place
		of dummy routines.

Bugs:		Exiting from SID with ^C leaves the console
		redirected to TTY: (unless the BIOS improperly
		restores the IOBYTE on warmboots).  The
		recommended fix is simply to exit with a "G0".
		Should you happen to hit ^C, reload SID and reset
		the IOBYTE to its original value, then exit with
		^C from the CRT terminal.

Remarks:	1. Although it would be possible to trap the
		warmboot and restore the IOBYTE, it's difficult to
		do correctly.  Trapping 0001h violates the basic CP/M
		addressing convention, making it impossible to
		run other resident modules that need to locate the BIOS
		and BDOS.  Trapping the warmboot at the BIOS jump
                vector does preserve addressing, but it still requires
		special efforts to maintain compatibility with any higher
		resident modules, and the trap must remove itself
		without disturbing them.  Since the application here
		is manual, interactive debugging, it seems best to
		favor compatibility and do a manual restoration.

		2. The assembler portion of SID/ZSID can be removed
		with the "-A" command to gain 680h bytes, but
		this must be done BEFORE loading SID2TTY.

Version:	1.0	--	10 October 1984	B. Mitchell

Revisions:	Please forward any revisions and improvements
		to the author.

Author:		Bridger Mitchell
		Plu*Perfect Systems
		Box 1494, Idyllwild CA 92349
		(714) 659-4432

Note:		Not tested on CP/M 3.0.