CP/M Interface

CP/M provides a universal interface linking application programs into the operating system. Through a system of calls to one location (0005 Hex) with the CPU register C set to the call number, the ROM-based operating system in HUNTER will implement the function and return to the user program. HUNTER is therefore compatible with many readily available commercial products,conforming to these standard system calls.

System Calls

CP/M system calls fall into two distinct categories. They are console (e.g. keyboard/LCD display) I/O and file I/O. Files are organised as CP/M disk files and may be accessed through a file control block (FCB).

Call No.	Name	Call No.	Name
0	System Reset	19	Delete File
1	Console Input	20	Read Sequential
2	Console Output	21	Write Sequential
3	Reader Input	22	Make File
4	Punch Output	23	Rename File
5	List Output	24	Return Login Vector
6	Direct Console I/O	25	Return Current Disk
7	Get I/O Byte	26	Set DMA Address
8	Set I/O Byte	27	Get Addr(Alloc)
9	Print String	28	Write Protect Disk
10	Read Console Buffer	29	Get R/0 Vector
11	Get Console status	30	Set File Attributes
12	Return Version Number	31	Get Addr(Disk Parms)
13	Reset Disk System	32	Set /Get User Code
14	Select Disk	33	Read Random
15	Open File	34	Write Random
16	Close File	35	Compute File Size
17	Search for First	36	Set Random Record
18	Search for Next	37	Reset Drive

System calls 38-47 refer to HUNTER operating system only.

File Control Block

The FCB contains 36 bytes of information on the current file being accessed. On HUNTER, the default FCB location is at 005CH, containing the following Information :-

Byte	Description
1	Drive code (zero)
2-9	Eight Character ASCII filename
10-12	ASCII file extension
13	Current extent number
14-15	Reserved
16	Record count for extent
17-32	Reserved for system use
33	Current record in sequential file operation
34-36	Random record number

HUNTER System Calls

This manual does not contain an exhaustive description of each system call, since they are defined and explained in great depth in many other publications. However, there does follow a brief description of each call, together with details of extra calls specific to HUNTER.

The C register is loaded with the call number plus any other parameters into other registers, and the A call is made to address 0005. Registers not mentioned are irrelevant on entry, and none are necessarily preserved on exit. For making these calls from Basic, see the CALL and ARG and Machine Code Calls.

Function	Call No	Entry	Exit	Remarks
System Reset	0	None	None	A system restart, re-entering HUNTER’S operating system.
Console Input	1	None	A=ASCII character	Read keyboard and echo onto screen. The call will wait until a key is pressed.
Console Output	2	E=ASCII character.	None	The character is displayed on the screen at the location of the cursor.
Reader Input	3	None	A=ASCII character.	The next character is read from the serial I/O buffer.
Punch Output	4	E=ASCII character.	None	The character is sent out through the serial port.
List Output	5	E=ASCII character.	None	As call 4.
Direct Console I/O	6	E=0FFH for input, E=ASCII character for output.	A=ASCII character if input, A=status if output.	Similar to calls 1 and 2, but there is no automatic echo to the screen. If a character is not ready from the keyboard then A=00 on return.
Get I/O Byte	7	None	A=I/O status.	The present I/O status byte is returned.
Set I/O Byte	8	E=I/0 value.	None	I/O byte is set.
Print String to Console	9	DE=string address.	None	An ASCII string whose start address is loaded into DE, is displayed on the screen. The string must be terminated with “$”.
Read Console	10	DE=buffer address.	None	The keyboard is read and the characters are placed into a buffer, the start address having been loaded into DE. The first byte contains the maximum number of characters to read into the buffer, the second byte contains the number of characters that have been placed into the buffer when input has been terminated with C/R or L/F. See Read Console Buffer for for further information.
Get Console Status	11	None	A=console status.	If a character has been typed in then 01H is returned, OOH if not.
Return Version Number	12	None	HL=version number.	HUNTER is CP/M version 2.2 compatible, so 0022H is returned.
Reset Disk System	13	None	None	The filing system is reset, and the DMA address is returned to 80H.
Select Disk	14	None	None	HUNTER has “RAM disks” so this call produces no action.
Open File	15	DE=FCB address.	A=directory code.	The file specified by the FCB is opened. If successful A=0,1,2 or 3. If not, then A=0FFH.
Close File	16	DE=FCB address.	A=directory code.	If successfully closed, A=0,1,2 or 3, otherwise A=0FFH.
Search for First	17	DE=FCB address.	A=directory code.	The directory is searched for the first match of the FCB. A=0FFH if there is no match, and 0,1,2 or 3 if there is. The filename is returned into the current DMA buffer. The search function returns the complete entry from the buffer.
Search for Next	18	None	A=directory code.	Similar to CALL 17, except that the next entry is looked for. The search function returns the complete entry from the buffer.
Delete file	19	DE-FCB address.	A=directory code.	Files which match the FCB are deleted. If none exist A=0FFH is returned.
Read Sequential	20	DE=FCB address.	A=directory code.	The specified file is read, and the sector copied to the current DMA address. A=00 for a successful read.
Write Sequential	21	DE=FCB address.	A=directory code.	The record at the current DMA address is written to the disk. A=00 indicate a successful write.
Make File	22	DE=FCB address.	A=directory code.	The specified file is created. A=0-3 if successful, or A=0FFH if not.
Rename a File	23	DE=FCB address.	A=directory code.	The file specified in the first 16 bytes of the FCB is renamed to the name in the second 16 bytes.
Return Login Vector	24	None	HL=login vector.	HUNTER returns HL=1 and A=1, indocating a single disk system.
Return Current	25	None	A=current disk.	Zero is always returned on HUNTER.
Set DMA Address	26	DE=DMA address.	None	The current disk data buffer area is set to DE.
Get Allocation Address	27	None	HL =allocation address.	Zero only is returned.
Write Protect Disk	28			Returns with no effect.
Get Read Only Vector	29			Returns with no effect.
Set File Attributes	30	DE=FCB address.	A=directory code.	File attributes for readonly etc. are set or reset as specified.
Disk Parameter Address	31	None	HL=disk parameter block address.	Disk parameters are returned which indicate a double sided double density disk. This is to allow for expansion within HUNTER. it should not be used for space calculation purposes.
Get or Set User Code	32			Returns with no effect.
Read Random	33	DE=FCB address.	A=directory code.	The file is read at the specified record. Normally non zero directory codes mean an error.
Write Random	34	DE=FCB address.	A=directory code.	The file is written at the specified record. A=0 means a successful write.
Compute File Size	35	DE=FCB address.	None	Random record field set to one plus the last record.
Set Random Record	36	DE=FCB address.	None	Random record field set.
Reset Drive	37	DE=drive vector.	None	HUNTER’S filing sytem is reset.
Set up the RS-232 Serial Port	38	None	None	The software setup routine is entered to set up the serial comm communications.
Initialise the Clock	39	None	None	The time and date buffer RAM is copied to the clock.
Write Random with zero fill	40	DE=FCB address.	A=directory code.	The write random with zero fill operation is similar to function 34, with the exception that a previously unallocated block is filled with zeros before data is written. NOTE: on early HUNTERs, this call was used for a different function.
Initialise Communications	41	None	None	This call allows configuration of the communications exactly as the standard initialise HUNTER communications routine.
Serial Status	42	None	A=port status.	To test for pending serial input characters A=0 for no characters read else A is non-zero.
Terminal emulation call	43	None	None	Enters terminal terminal emulation mode.
Wand input call	44	DE=Buffer Address	None	The Wand code is selected previously by setting the bartype location according to wand code being read. The code is read into the buffer. The user must provide the buffer address and, in the first location of the buffre, the user must provide the maximum number of characters to be read into the buffer. On exit, the second byte of the buffer contains the number of that have been placed in the buffer, followed by the wand character’s input.
Fetch key without echo	47	None	A=ASCII code of character.
Read the Clock	48	None	None	The time and date is copied from the clock into the time and date buffer RAM (see Memory Locations) locations TENTHSEC to TENYR.