grrr.. correct technique to read disk channel..

still hindering me.. i cannot get $90 to report nothing except "0" and posting the source probably wont help...

You would open 2 files. One does the I/O of bytes, the other is the command channel.
This is exactly how you find commodore did this in their implementation, the routines to boot a disk in drive 8 use 2 open channels at the same time.
I am not sure what would help you, so I'm including a bunch.
Here is an except of the C1541-II manual (page 80)

Imagine we open a file, the MC equivalent of basic: open 3,8,0, "TEST"
SETLF = $FFBA ; set logical chl, iec nr and 2nd adress
SETNAM = $FFBD ; len and addr of fnam
OPEN = $FFC0 ; open logical file
CLOSE = $FFC3 ; close logical file
CHKIN = $FFC6 ; channel to use for Input
CHKOUT = $FFC9 ; channel to use for output
CLRCHN = $FFCC ; back to normal channels
CHRIN = $FFCF ; one byte from selected channel
CHROUT = $FFD2 ; one byte to selected channel

START
LDA #4 ; len of fnam
LDX #<FNADR ; low bye of fnam
LDY #>FNADR ; hi byte
JSR SETNAM
LDA #3 ; logical file number
LDX #8 ; device number
LDY #0 ; secondary address
JSR SETLFS ; set A,X,Y
JSR OPEN ; try to open file so open 3,8,0,"TEST"
if this fails, then at this point you must check for carry set and inspect value for A
LDX #3
JSR CHKIN ; select file 3 for input
if this fails, then at this point you must check for carry set and inspect value for A
NEXT
JSR CHRIN ; get next byte from file
BEQ END ; until finish (ie. A = 0 means end of file)
JSR CHROUT ; output to screen
JMP NEXT
;
END
LDA #3
JSR CLOSE
JSR CLRCHN
RTS

FNADR .BYT "TEST" ; file name
---
From the above we see the official document Commodore suggested way to input a stream of bytes from disk.
The KERNAL must know what logical file (this is just your favorite number) the file name on a device and 2nd address is you want to open
The open command of the file may fail, of course.
Note that the example in the C64 Reference manual (equal for c128) is for a 'load' on a file, here it is an 'open'.
A 'load' gets the (whole) file to RAM while an 'open' means you end up looping to get the data yourself (until null)
For the C128, the 'load' allows for an improved speed to get at data!

Also, for the c128 one should (at some point) indicate the BANK (like the basic BANK command) one wants to use. For instance:
LDX #0
JSR SETBNK ; $FF68
This setting of the bank must be done before the IO calls. For instance your filename might be in a different banking (say, ram1) and the kernal will retrieve its info from there if you tell it to use that config.


Back to your question about the error handling. Assuming you use 'OPEN', this will attempt to send to the drive the information about the file you wish to work with. If you are successful in sending that info to the drive (because it is actually connected and on) then this will work fine. Of course, the drive will conclude things didn't work but unless you ask, you won't know (since it is its own computer).
The communication to the drive may fail as well.
Consider you set up the information for a file and at some point to tell the KERNAL to use the logical file (let's say you use logical file number 7, lucky seven), you have to connect "device 8" and "secondary channel 0" to that. Once you did that, you will find that an attempt to do a "CHKOUT" or "CHKIN" in that logical number may fail:
LDX #7 ; a logical number you previously have set up with SETLFS (A=7, X=8, Y=0)
JSR CHKOUT ; if your drive isn't on, this returns with Carry Set. If all is well, Carry will be Clear.
BCS hdlerror ; Carry Set means error (A = error code)
RTS

hdlerror:
; when CHKOUT failed (that is, CHKOUT returned with carry set)
; Fail means A = 0, 3, 5, 7
; 0 = stop key pressed (user)
; 3 = file not open
; 5 = device not present
; 7 = file not input (CHKIN) or output (CHKOUT)
CMP #5 ; device not present
BEQ retnok
CMP #3 ; file not open (no disk?)
BNE tryinit
retnok:
SEC ; set carry to indicate error
RTS ; return (A = 3 or 5, in any case you will need to read the error channel)

CMDSTR: .BYT "I"

tryinit: ; send an "I" command to the drive (clears errors and read BAM)
LDA #23
JSR CLOSE ; close file first (just in case)
LDA #0
JSR SETBNK ; kernal bank
LDA #1 ; len of cmd to send
LDX #<CMDSTR ; low bye of fnam
LDY #>CMDSTR ; hi byte
JSR SETNAM
LDA #23 ; logical file for command channel (just some number, could be 15 too)
; using 15 is customary and saves because A == Y
LDX #8 ; device 8
LDY #15 ; command channel as secondary
JSR SETLFS ; set A,X,Y
JSR OPEN ; try to open file so open 23,8,15,"I"
BCS tstA
; drive responds. So now you CHKIN to file 23 and read out the string
LDX #23
JSR CHKIN
NEXTch15
JSR CHRIN ; get next byte from cmd-channel
BEQ END ; until finish (ie. A = 0 means end of transmission)
JSR CHROUT ; output to screen
JMP NEXTch15
RTS

tstA:
CMP #5 ; no drive
BEQ print to tell user no drive
RTS

does it matter which register gets loaded to setbank?? u show LDX, then later.. LDA, ldx#0 , jsr setbnk or lda#0, jsr setbnk?? i've dealt with the bank # in other areas , but im more than likrly not doing it right...