The source code file “Manager.asm”, together with any included files it references, is responsible for defining a few key constants and providing a set of BIOS functions.
These constants should be defined in “Manager.asm”:
- BNAME
- kBiosID
- kBiosMajor
- kBiosMinor
- kBiosRevis
The BIOS name (BNAME) can be anything you like as long as it is no more than 15 characters long. The name appears in the SCM help text.
It would be best to ask me for a BIOS ID, but failing that, select a value over 100 to avoid conflicts with official SCM releases.
The BIOS version consists of three numbers, each between 0 and 9.
The following functions must be provided:
| Function | Descriptions |
| H_Test | Self-test |
| H_Init | Initialise |
| H_GetName | Get hardware name message |
| H_GetVers | Get version details |
| H_SetBaud | Set baud rate |
| H_IdleSet | Idle event set up |
| H_MsgDevs | Output device list message |
| H_RdRAM | Read from banked RAM |
| H_WrRAM | Write to banked RAM |
| H_CopyROM | Copy from banked ROM to RAM |
| H_ExecROM | Execute code in banked ROM |
| H_Delay | Delay by DE milliseconds |
Some of the functions are usually identical for all configurations of SCM and are provided in the file “Common.asm” in the “BIOS” folder tree.
Each function is specified below.
H_Test (Self-test)
Immediately the processor exits reset, execution jumps to the self-test function (H_Test). No other instructions are executed before the jump here. If the test passes, program execution should jump to “CStrt” (address 0x000C).
On entry: No parameters required
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' not specified
The self-test should do as much as possible, including a RAM test, before needing working RAM or using anything other than the absolute minimum of working hardware.
If the hardware supports some form of status indication it should be used to show the self-test code is running, and where possible to report any errors.
Typically, the test will show a light sequence on the digital status port to indicate code is running correctly. It should then do a very brief RAM test with failure indicated. Additional tests, such as checking there is a console device available, should be performed and failure again shown where possible. No attempt should be made to start the monitor if a fatal error occurs, such as faulty RAM.
H_Init (Initialise)
This function is called shortly after reset to initialise the BIOS and the hardware it supports.
On entry: No parameters required
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
The hardware flags (see H_GetVers) are usually set up by this functions.
H_GetName (Get hardware name message)
This function is included in “Common.asm” and returns a pointer to the BIOS name string.
On entry: No parameters required
On exit: DE = Pointer to BIOS name string
AF BC HL not specified
IX IY I AF' BC' DE' HL' preserved
H_GetVers (Get Version Details)
This function is included in “Common.asm” and returns version details.
On entry: No parameters required
On exit: D, E and A = BIOS code version
D = kBiosMajor
E = kBiosMinor
A = kBiosRivis(ion)
H, L = Target hardware ID and flags
H = kBiosID
L = Hardware option flags
F BC not specified
IX IY I AF' BC' DE' HL' preserved
Hardware flags are hardware specific but for most Z80/Z180 systems they are:
| Bit | Meaning |
| 0 | ACIA #1 detected |
| 1 | SIO #1 detected |
| 2 | ACIA #2 detected |
| 3 | Bit-bang serial available |
| 4 | CTC #1 detected |
| 5 | SIO #2 detected |
| 6 | CTC #2 detected |
| 7 | Z180’s integrated peripherals available |
H_SetBaud (Set baud rate)
If supported by the target hardware, serial port baud rate is set up for the specified console device.
On entry: A = Baud rate code (see table below)
C = Console device number (1 to 6)
On exit: If successful:
A != 0 and NZ flagged
If unsuccessful:
A = 0 and Z flagged
BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
Not all hardware supports baud rate setting and the hardware that does, may not support all the rates shown below.
If the specified console device and baud rate are not a valid combination or a hardware issue is detected, the function leaves the current settings unchanged and returns “unsuccessful” status.
| Serial Baud Rate | Rate Code | Alt Rate Code |
| 230400 | 1 | 0x23 |
| 115200 | 2 | 0x11 |
| 57600 | 3 | 0x57 |
| 38400 | 4 | 0x38 |
| 19200 | 5 | 0x19 |
| 14400 | 6 | 0x14 |
| 9600 | 7 | 0x96 |
| 4800 | 8 | 0x48 |
| 2400 | 9 | 0x24 |
| 1200 | 10 | 0x12 |
| 600 | 11 | 0x60 |
| 300 | 12 | 0x30 |
| 150 | 13 | 0x15 |
H_IdleSet (Idle event set up)
When the system is not busy it polls the idle events. Idle events allow simple background activity, such as flashing LEDs. This function sets up the idle event handler.
On entry: A = Idle event configuration:
0 = Off (no events supported)
1 = Software generated timers
2 = Hardware generated timers
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
This function normally sets up the system jump table idle handler (table entry 0x0C). The BIOS need not distinguish between requests for software or hardware generated timers. If the hardware or BIOS does not support hardware timers, then software timers should be set up instead. If hardware timers are always available the BIOS may use these instead of software generated timers.
The idle handler is called to poll for a 1 millisecond event .
On entry: No parameters required
On exit: If 1ms event to be processed:
NZ flagged and A != 0
Otherwise:
Z flagged and A = 0
BC DE HL preserved
IX IY I AF' BC' DE' HL' preserved
H_MsgDevs (Output devices message)
The monitor’s DEVICES command lists hardware devices which have been detected or is assumed to be present. This function outputs the list to the current console device.
On entry: No parameters required
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
H_RdRAM (Read from banked RAM)
Systems that support a simple two RAM bank memory map, such as SC108 and SC114, can read a byte from the secondary bank with this function.
On entry: DE = Address in secondary bank
On exit: A = Byte read from RAM
F BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
Only the RAM that can be mapped into memory at the same time as the SCM ROM can be read with this function. Typically this means only address from 0x8000 to 0xFFFF.
Systems that do not have a suitable memory map should implement a dummy function that just returns without doing anything.
H_WrRAM (Write to banked RAM)
Systems that support a simple two RAM bank memory map, such as SC108 and SC114, can write a byte to the secondary bank with this function.
On entry: A = Byte to be written to RAM
DE = Address in secondary bank
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
Only the RAM that can be mapped into memory at the same time as the SCM ROM can be written with this function. Typically this means only address from 0x8000 to 0xFFFF.
Systems that do not have a suitable memory map should implement a dummy function that just returns without doing anything.
H_CopyROM (Copy from banked ROM to RAM)
Systems that support banked ROM, such as LiNC80 SBC1, can copy a block of memory from any ROM bank to RAM.
On entry: A = ROM bank number (0 to n)
HL = Source start address (in ROM)
DE = Destination start address (in RAM)
BC = Number of bytes to copy
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
H_ExecROM (Execute code in banked ROM)
Systems that support banked ROM, such as LiNC80 SBC1, can select the specified bank and execute code the in that bank.
On entry: A = ROM bank number (0 to n)
DE = Absolute address to execute
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
The address executed is the absolute address in the 64k memory map when the specified ROM bank is mapped into memory. It is not the address from the start of the ROM chip.
The code is executed by calling it, so it should end with a RET instruction.
H_Delay (Delay by DE milliseconds)
This function is included in “Common.asm” and is a software delay of the specified number of milliseconds.
On entry: DE = Delay time in milliseconds
On exit: AF BC DE HL not specified
IX IY I AF' BC' DE' HL' preserved
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