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Interis 64 Developer Notes

The information in this document will be invaluable to developers writing software for Interis 64.

Memory Map

Address Function
$FFFF System call number
$FFFE SLOT 7 Hardware ID
$FFFD SLOT 6 Hardware ID
$FFFC SLOT 5 Hardware ID
$FFFB SLOT 4 Hardware ID
$FF80-$FFEF System call vector table
$FF10-$FF7F System scratchpad memory
$FF0E Interrupt 7 Vector
$FF0C Interrupt 6 Vector
$FF0A Interrupt 5 Vector
$FF08 Interrupt 4 Vector
$FF06 Interrupt 3 Vector (RTC/NVRAM)
$FF04 Interrupt 2 Vector (Serial Port)
$FF02 Interrupt 1 Vector (Keyboard)
$FF00 Interrupt 0 Vector (Unused)
$F400-$FEFF Code for system calls
$F000-$F399 Video Driver: 1KB
$EC00-$E999 Sound Driver: 1KB
$E800-$EB99 Storage Driver: 1KB
$E800 Starting address of stack pointer
$0100-$E800 Application memory
$0000-$00FF Reserved for Z80 reset vectors

Hardware IDs

Each of the expansion slots can accept any sort of expansion card. The four Hardware ID memory slots ($FFFB-$FFFE) are populated by the card initialization routines to identify which optional hardware is in which slot.

By convention, Hardware IDs are assigned by device category, as follows:

Hardware ID Device Type
$00 - $0F Reserved for built-in devices
$10 - $1F Video and display devices
$20 - $2F Sound and music devices
$30 - $3F Data storage devices
$40 - $4F Human interface devices
$50 - $5F Communication devices
$60 - $6F Data Processing devices
$70 - $FF Other devices

Currently Assigned Hardware IDs

Note: Some of the devices listed here are in-development and are unsupported.

Video and Display Devices

  • $10 - TMS9918A Video Card
  • $11 - Graphic LCD Driver Card
  • $11 - Character LCD Driver Card

Sound and Music Devices

  • $20 - Yamaha OPL2 Sound Card
  • $21 - SN76489 Sound Card

Data Storage Devices

  • $30 - WD37C65C Floppy Disk Controller Card
  • $31 - Secure Digital Adapter Card
  • $32 - CompactFlash Adapter Card

Human Interface Devices

  • $40 - Game Controller Card
  • $41 - PC Joystick Card

Communication Devices

  • $50 - Parallel Port Card

Data Processing Devices

  • $60 - AM9511A Math Coprocessor Card

System Calls

To make a system call (syscall), load the system call number into memory at $FFFF and issue a RST $10 instruction. See the documentation for each syscall below for information on passing parameters and results.

Call Number Function
$00 Warm Reset
$02 Disk Boot
$04 Start Debug Monitor
$06 Print character to output device
$08 Print null-terminated string to output device
$0A Read a character from BufferedInput
$0C Check if there's a character available in BufferedInput
$0E Write a character into the input buffer
$10 System Bell
$12 NVRAM Read Byte
$14 NVRAM Write Byte
$16 Serial Send Byte

$02 – Reset

Clears the input buffer, clears the screen, displays the ROM header message, attempts to boot from a storage device, falls back to the system monitor if that fails.

$04 – Start Debug

Breaks out of the current program to the system monitor for debugging.

$06 – Print character to output device

Writes the byte of data in the A register to the primary output device. By default, this is the serial port, but hardware drivers may override this call to become the default device.

$08 – Print null-terminated string to output device

Writes a string of characters starting at (HL) to the primary output device via repeated calls to syscall $06. Execution continues until a null byte is encountered, which is not sent. See the documentation for syscall $06 for information on output devices.

$0A – Read a character from BufferedInput

Removes the first character from the input buffer and stores it in the A register. If no character is available in the buffer, this call will block until one becomes available.

$0C – Check if there's a character available in BufferedInput

Checks to see if there are characters in the input buffer. If there are characters in the buffer, the Z flag will be cleared, otherwise Z will be set. Additionally, A will contain the number of characters in the buffer.

$0E – Write a character into the input buffer

Inserts the character in the A register into the input buffer. If the input buffer is full, this call is silently ignored.

$10 – System Bell

Sounds the system bell. By default this is a simple beep from the on-board speaker generated by the NVRAM chip. Audio device drivers can override this call to provide their own system bell.

$12 – NVRAM Read Byte

TODO: Document system call

$14 – NVRAM Write Byte

TODO: Document system call

$16 – Serial Send Byte

Writes the byte of data in the A register to the serial port. By default, this is the same as syscall $06, but this is made available separately for cases where the default output has been redirected by a device driver.

$18 – Serial Receive Byte

Receives a byte of data from the serial port in the A register. By default, this points to BufferedInput.Accept, so serial data is passed through the input buffer. Applications can overwrite this to handle serial data on their own.