Yes, this was the same experience I had on my real hardware, even with SAVE "CS1",IV254 - it just displays I/O Error 03.
Well this is the problem with GROM 0 of the TI99/4A as it has restrictions built in....
TI INTERN MANUAL GROM 0
1387 : CZ @>834E Logical record length
1389 : BR GROM@>1391
138B : ST VDP@>FFFA(@>8356),>40 Decimal 64 default value
1391 : ADD VDP@>FFFA(@>8356),>3F
1397 : AND VDP@>FFFA(@>8356),>C0 Round to integer number 64
GROM 0 rounds to a values of 32 or 64, thus 254 will error out for RXB use of SAVE "CS1",IV254
Now RXB 2001 up to 2015 does have:
CALL IO(4,number of bytes,VDP-address)
There are no prompts as this is direct CRU Cassette control so this does not use any GROM 0 GPL.
Thus you would need to write a XB program to run this routine, so would need to be merged with current XB program.
And of course is limited to the amount of VDP RAM free.
Now for example from COMMAND mode:
1. type in a program to save. (I used AMSTEST as a test program)
2. type: CALL I0(3,8,12,1) :: CALL IO(4,3884,10411)
3.turn on Cassette RECORD
4. press ENTER
5. When you hear no more sound from speaker STOP CASSETTE
Line 2 turns ON the Audio CRU line so you can hear the RECORDING.
Also in line 2 3884 bytes are written to Cassette from 10411 up to 14295 into VDP RAM
Edited by RXB, Sat Jun 9, 2018 8:49 AM.