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Basic I/O System (BIOS) Functions
STANDARD BIOS SUBROUTINE ENTRY POINTS
This section describes the standard BIOS subroutines: system initialization subrou-
tines, simple character 1/0 subroutines, and disk 1/0 subroutines.
System Initialization Subroutines
ARRIVE HERE FROM COLD BOOT
ENTRY.
FUNCTION 0
INIT
RETURN
This subroutine is called directly by the
CP/M-86
loader after the CPM.SYS file has
been read into memory. The procedure performs any hardware initialization not
performed by the bootstrap loader (see below for a discussion of hard <;lisk initiali-
zation), sets initial values for BIOS variables (including IOBYTE), prints sign-on
messages, and initializes the interrupt vector to point to the BDOS offset (OB06H)
and base.
For hard disk systems, this subroutine initializes hard disk processing. It first
checks the DMA controller to determine whether the hard disk adapter is installed.
lfit exists, the routine waits to allow the hard disk units to warm up. The procedure
then generates the system unit table (SYSUNITID), sets the number of hard disk
drives, reads the error map from the hard disk, and initializes the values for BIOS
variables.
When the routine is complete, it jumps to the CCP offset (OlH). All segment
registers are initialized at this time to contain the base of the operating system.
ARRIVE HERE FOR WARM START
ENTRY.
FUNCTION 1
WBOOT
RETURN
This subroutine is called whenever a program terminates by performing a BDOS
function 0 call. Some reinitialization of the hardware or software may occur here.
When this routine completes, it jumps directly to the warm start entry point of the
CCP (06H).
5-5
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