CP/M Basic Input/Output System
The BIOS is the machine-dependent part of CP/M. In theory, all you need
to do is change the BIOS and CP/M will work on a different machine. The same
used to be true of MSDOS...
The BIOS begins with the following jumps to service routines:
JMP BOOT ;Cold start routine
JMP WBOOT ;Warm boot - reload command processor
JMP CONST ;Console status
JMP CONIN ;Console input
JMP CONOUT ;Console output
JMP LIST ;Printer output
JMP PUNCH ;Paper tape punch output
JMP READER ;Paper tape reader input
JMP HOME ;Move disk head to track 0
JMP SELDSK ;Select disk drive
JMP SETTRK ;Set track number
JMP SETSEC ;Set sector number
JMP SETDMA ;Set DMA address
JMP READ ;Read a sector
JMP WRITE ;Write a sector
In CP/M 2 and later, the following extra jumps appear:
JMP LISTST ;Status of list device
JMP SECTRAN ;Sector translation for skewing
In CP/M 3, a further set of jumps is present:
JMP CONOST ;Status of console output
JMP AUXIST ;Status of auxiliary input
JMP AUXOST ;Status of auxiliary output
JMP DEVTBL ;Address of devices table
JMP DEVINI ;Initialise a device
JMP DRVTBL ;Address of disks table
JMP MULTIO ;Read/write multiple sectors
JMP FLUSH ;Flush host buffers
JMP MOVE ;Move a block of memory
JMP TIME ;Real time clock
JMP SELMEM ;Select memory bank
JMP SETBNK ;Select bank for DMA operation
JMP XMOVE ;Preload banks for MOVE
JMP USERF ;System-depedent functions
JMP RESERV1 ;Reserved
JMP RESERV2 ;Reserved
This function is completely implementation-dependent and should never be
called from user code.
Reloads the command processor and (on some systems) the BDOS as well.
How it does this is implementation-dependent; it may use the reserved tracks
of a floppy disc or extra memory.
Returns its status in A; 0 if no character is ready, 0FFh if one is.
Wait until the keyboard is ready to provide a character, and return it in A.
Write the character in C to the screen.
Write the character in C to the printer. If the printer isn't ready, wait
until it is.
Write the character in C to the "paper tape punch" - or whatever the
current auxiliary device is. If the device isn't ready, wait until it is.
Read a character from the "paper tape reader" - or whatever the
current auxiliary device is. If the device isn't ready, wait until it is.
The character will be returned in A. If this device isn't implemented, return
character 26 (^Z).
Move the current drive to track 0.
Select the disk drive in register C (0=A:, 1=B: ...). Entered with DE=0 or
FFFFh. If DE=0, the disc will be logged in; if it is FFFFh, no attempt will
be made to read it.
SELDSK returns the address of a Disc Parameter Header in HL.
Set the track in BC - 0 based.
Set the sector in BC. Under CP/M 1 and 2 a sector is 128 bytes. Under
CP/M 3 the sector size is given in the Disk Parameter Block.
The next disc operation will read its data from (or write its data to) the
address given in BC.
Read the currently set track and sector
Write the currently set track and sector. C contains a deblocking code:
C=0 - Write can be deferred
C=1 - Write must be immediate
C=2 - Write can be deferred, no pre-read is necessary.
Return status of current printer device.
Returns A=0 (not ready) or A=0FFh (ready).
Translate sector numbers to take account of skewing.
On entry, BC=logical sector number (zero based) and DE=address of translation
table. On exit, HL contains physical sector number.
Return status of current screen output device.
Returns A=0 (not ready) or A=0FFh (ready).
Return status of current auxiliary input device.
Returns A=0 (not ready) or A=0FFh (ready).
Return status of current auxiliary output device.
Returns A=0 (not ready) or A=0FFh (ready).
Return in HL the address of the devices table, or 0 if the devices table
isn't implemented. The devices table contains 13 entries, one for each
character device. Each entry is formed:
DEFB 'NAME ' ;Name, 6 bytes. Zero if this device is
;not used.
DEFB mode ;Bitmapped value:
;Bit 0 set => can input from this device
;Bit 1 set => can output to this device
;Bit 2 set => can change the baud rate
;Bit 3 set => supports XON/XOFF
;Bit 4 set => is using XON/XOFF
;Bits 5,6,7 set to 0.
DEFB baudrate ;Coded speed, 1-15 or 0 if speed can't be
;changed.
;Rates are 50,75,110,134.5,150,300,600,1200,
; 1800,2400,3600,4800,7200,9600,19200.
Initialise character device number C - called when the device's settings
(baud rate, mode etc.) are changed.
Return in HL the address of the drive table, or 0 if the drive table
isn't implemented. The drive table contains 16 pointers to the Disc Parameter
Headers of the 16 disc drives A-P; if a pointer is 0 it means that the
corresponding drive does not exist.
The drive table is usually (but not always) in common memory (ie accessible
by user programs).
Set the number of sectors read/written by one call to READ
or WRITE.
Please tell me if you know precisely how this function works. (See note on my homepage for email address.)
Flush any deblocking buffers.
Returns A=0 if successful, 1 for physical disc error, 2 for drive R/O.
Please tell me if you know precisely how this function works. (See note on my homepage for email address.)
Move BC bytes of memory, from the address in HL to the address in DE.
Should return HL and DE pointing to the first addresses not copied. If
XMOVE is used before this function, data are moved
between two memory banks.
Get the current date and time into the 5 bytes pointed to by address
BC. HL and DE must be preserved.
The format of the 5-byte buffer is:
DW day ;Day 1 is 1 Jan 1978
DB hour ;packed BCD
DB minute ;packed BCD
DB second ;packed BCD
Set the current bank to the number in A. Bank 1 is the bank in which
user programs run (the TPA); Bank 0 and any other banks are used by CP/M for
disc buffers or as a RAMdisc.
Set the bank to be used for the next read/write sector operation. The bank
number is passed in A.
After XMOVE, the next call to MOVE will move
data between different memory banks. Call XMOVE with C=source bank
and B=destination bank.
This function is reserved for the author of the BIOS to add any extra
features. On Amstrad computers, for example, this call accesses the
extended BIOS functions.
These calls are reserved and contain JMP 0 instructions.
