System information

Table 6-5. (continued)
Entry Point Function
SETSEC Register BC contains the sector number, 1 through 26, for subsequent disk
accesses on the currently selected drive. The sector number in BC is the
same as the number returned from the SECTRAN entry point. You can
choose to send this information to the controller at this point or delay
sector selection until a read or write operation occurs.
SETDMA Register BC contains the DMA (Disk Memory Access) address for
subsequent read or write operations. For example, if B = 00H and C = 80H
when SETDMA is called, all subsequent read operations read their data
into 80H through 0FFH and all subsequent write operations get their data
from 80H through 0FFH, until the next call to SETDMA occurs. The
initial DMA address is assumed to be 80H. The controller need not actually
support Direct Memory Access. If, for example, all data transfers are
through I/O ports, the CBIOS that is constructed uses the 128byte area
starting at the selected DMA address for the memory buffer during the
subsequent read or write operations.
READ Assuming the drive has been selected, the track has been set, and
the DMA address has been specified, the READ subroutine attempts to
read eone sector based upon these parameters and returns the following
error codes in register A:
0 no errors occurred
1 nonrecoverable error condition occurred
Currently, CP/M responds only to a zero or nonzero value as the return
code. That is, if the value in register A is 0, CP/M assumes that the disk
operation was completed properly. IF an error occurs the CBIOS should
attempt at least 10 retries to see if the error is recoverable. When an error
is reported the BDOS prints the message BDOS ERR ON x: BAD
SECTOR. The operator then has the option of pressing a carriage return to
ignore the error, or CTRL-C to abort.
6.6 BIOS Entry Points CP/M Operating System Manual
6-23