SVI uses same 8255 PPI as MSX. Both machines use "MODE 0" communication, but it has different function in the system.

Here is how it is connected:

Mode select I/O Port address #97 (out) / #9B (in)

The ports A and B are input and port C is output. This means that in any normal situation the mode select byte should be #92 (See 8255 manual) Exception to this rule is how ever, if computer needs to communicate outside trough joystick ports (ie. while reading graphics pad). In this case the port A can be changed to output (Mode select byte = #82) Please note: Writing mode byte will reset the ports and therefore turn cassette motor on.

This port can be used also to toggle bits in port C. (See 8255 manual)

Port A I/O Port address: #98 (In) / #94 (Out)

• Bit 7: Cassette: Read data
• Bit 6: Cassette: Ready status
• Bit 5: Joystick 2: Trigger (pin 6)
• Bit 4: Joystick 1: Trigger (pin 6)
• Bit 3: Joystick 2: EOC (pin 9)
• Bit 2: Joystick 2: /SENSE (pin 5)
• Bit 1: Joystick 1: EOC (pin 9)
• Bit 0: Joystick 1: /SENSE (pin 5)

Please see: SVI-3x8 Joystick port

Port B Input Port address: #99

• Bit 7: Keyboard: Column status of selected line
• Bit 6: Keyboard: Column status of selected line
• Bit 5: Keyboard: Column status of selected line
• Bit 4: Keyboard: Column status of selected line
• Bit 3: Keyboard: Column status of selected line
• Bit 2: Keyboard: Column status of selected line
• Bit 1: Keyboard: Column status of selected line
• Bit 0: Keyboard: Column status of selected line

Please see: SVI-3x8 keyboard

Port C output Port address: #96

• Bit 7: Key click sound output (pulse)
• Bit 6: Cassette: Audio output (1=Audio output enabled, only available in SV-903, not in SV-904)
• Bit 5: Cassette: Write data
• Bit 4: Cassette: Motor relay control (0=on, 1=off)
• Bit 3: Keyboard: Line select 3
• Bit 2: Keyboard: Line select 2
• Bit 1: Keyboard: Line select 1
• Bit 0: Keyboard: Line select 0