[net.micro] CP/M BDOS

chris@Rand-Unix@sri-unix (09/09/82)

I would be interested to know if there is a source of information detailing
at somewhat greater length than the table in Thom Hogan's Osborne CP/M
User Guide exactly what the input/output parameters require for CP/M
BDOS calls in assembly programming.  In particular the file manipulation
funcitons and the complexities of the file control block (FCB) have me
bewildered.  There is a "default FCB" located at OC5 hex with 36 bytes
of information.  Is this automatically changed by something else, or by
BDOS calls, or does one have to move a new FCB into this location to access
a new file?  Or is there a way to specify a different FCB at a different
address?

Thanx

chris mcmenomy (chris@rand-unix)
Rand Corp.

netnews (09/10/82)

I dont know anything about Osborne CP/M, but there are obvious answers to
all of your questions concerning standard CP/M. I would recommend the
Digital Research Guide to CP/M Interface with the proviso that you COULD
have to review the addresses for your particular implementation.
To answer your major questions:
CP/M uses only the default DMA address and FCB, but allows an interface
to change either. If changed, any disk access will use the current DMA
address (presuming that you dont restart the system) and you (the user)
specifies the FCB address in the BDOS call.
	John Beal
		either at the address shown in the header
		(except this machine will be down all next week)
	or whuxg!beal
		or Bell Labs Whippany NJ 201-386-5060