nessus@nsc.UUCP (Kchula-Rrit) (06/05/85)
["With such a weapon I could boil the Earth to vapor."]
A few days ago, someone on the network gave me a short "example-type
program to illustrate the use of CALL LOAD and CALL LINK to load and run
machine-language programs from XBASIC. The program does a couple of writes to
the video chip to set its mode from graphics mode, what [X]BASIC normally runs
in, to text mode which produces a display width of 40 columns. The display
came out garbled because the OS used the new screen width but XBASIC still
though the display was 32 columns, but I could count the number of columns.
The idea of using a 40-column display from XBASIC fascinates me, but I
do not know enough about the internal workings of the video chip to get the
screen image to come out right and am concerned about the possibility of
damaging the video chip by sending the wrong data to the wrong place in the
wrong way.
Does anyone out there know how the TMS9918(A) video chip used in the
TI 99/4A works? In particular, I would like to know how to access the internal
registers and external RAM that the chip uses. How does one do this on a
machine instruction basis?
My editor/assembler manual contains info on doing video reads and writes,
but it assumes that the user is going through the operating system with the
E/A. I am trying to do this by running a small machine-language program
to/from XBASIC because I do not have the E/A. The reason that I bought the
manual is to gather more info about the console's internal workings and it has
helped, but in this case...
The local TI distributor has said "Let me look up the part number for
the user's manual and call you back when I have price/availability info."
I haven't heard anything since...
From the alter ego of--
Kchula-Rrit
!menlo70!nsc!nessus