		COMTAL DRIVER & ACCESS CODES & TEST CODES

		Bob Brown NCAR Boulder,Colorado
		(303)-494-5151  X 718

This directory contains the driver source for the Comtal display.
THERE ALSO ARE CODES TO TEST THE DRIVER AND ACCESS CODES .

The device is considered to be one controller with several units.
There are 3 units for images CD0,CD1,CD2 of which 0+1 are on-line
and the third does not exist. There is one unit for each COLOR &
 FUNCTION memory and a unit for each 4 GRAPHICS planes.
 A 16th unit is allocated
for special functions,ie.LSI-11 RAM and COMTAL ASCII command strings.

With this driver the Comtal display can be treated as a fixed head disk
,ie. INI , MOU , DMO , PIP all work with it as a files-11 volume.
Major problem here is crummy memory has too many parity errors to 
be usefull,ie. generates checksum errors on files.

Normally graphics programming is carried out using the Fortran access
codes which were used with the NOVA. These somewhat clumsy codes are
handy only because they funtionally isolate the features used.
	COM0-send transfer command zero ,ie. set up display mux
	COM1-send trans 1 ,ie. images + graphics
	COM1XX-identical to COM1 except the user must issue a WAITFR
		on the lun. This is used where high speed loading
		via DOUBLE buffers is required. In animated movie loops
		use this and a 2 buffer scheme from the disk.
	COM2-send trans 2 ,ie. color + functon memories + programmable target
	COM3-send ascii strings, load LSI-11 memory,read X/Y coords.

The multi-unit approach was taken to allow eventually multi-users on one
COMTAL , using RSX-11M to keep the images seperated. This requires a 
new output MUX switch on the COMTAL to drive multiple monitors with
different image mixes.

NOTE:the driver supports the ERRLOGGER by calling $DEVER when the err
bit is on in the CSR at the end of an operation. This feature is super
for recording malfunctions. The driver also supports timeouts via
$DEVOT in case the Comtal does not respond after 2 seconds.

NOTE:the only features that currently dont funtion are the loading of 
LSI-11 memory from the host, this is mode 3 and its not well explained
in the hardware manual. Also the 'send message' command from VISION 1 to host is not 
supported and will cause an unexpected intterupt to host.


NOTE:	User should modify CDRTB.MAC to reflect the number of images & 
graphics planes they have , ie. set OFFLINE in the data base those planes
not present.

NOTE:The access package COMTAL.FTN expects the lun for the comtal to be 
lun = 4 for all operations. It is reassigned for each COMx call.


SUBROUTINES DMEM,DSEND,DCMD,DBUF ARE TEST CALLS TO COMX CODES. THEY ARE
PROVIDED AS A CONVEINIENT METHOD TO EXERCIDE COMTAL.FTN WHICH IN TURN
EXECISES CDDRV. EACH ROUTINE AS DMEM EXECISES 1 TYPE COMTAL DRIVER,IE.
COM1(..,...,..,). THEY ALSO SHOW HOW COMX MAY BE CALLED.---THESE ARE
NOT MODEL TEST ROUTINES ONLY QUICKIES------------------
