The Master Component's cartridge port consists of a single 44-pin 0.1" spacing edge-card connector. A number of essential bus signals are brought out on this connector. The following figures illustrate which of these signals corresponds to each of the various cartridge pins. The table afterwards lists what each signal does.
Pin Mapping on Intellivision Cartridge Port
|Component Side (Top)||Solder Side (Bottom)|
|Intellivision I: Ground||GND||2||1||GND||Ground.|
|Intellivison II: System Changer External Video||Ext. VIDEO|
|Intellivoice Serial Bus: Control 1||C1|
|Character BLaNK||CBLNK||4||3||~MSYNC||Master SYNC.|
|Intellivoice Serial Bus: Control 2||C2|
|External Audio Input.||Ext. AUDIO||6||5||DB7||Bit 7 of the Address / Data Bus.|
|External Video Input. (Intellivision I only)||Ext. VIDEO||8||7||DB8||Bit 8 of the Address / Data Bus.|
|Master CLocK.||MCLK||10||9||DB6||Bit 6 of the Address / Data Bus.|
|Reset input.||RESET||12||11||DB9||Bit 9 of the Address / Data Bus.|
|Timing signal from the STIC.||SR1||14||13||DB5||Bit 5 of the Address / Data Bus.|
|Intellivoice Serial Bus: Serial Output||SER OUT|
|Intellivoice Serial Bus: Control 3||C3||16||15||DB10||Bit 10 of the Address / Data Bus.|
|Intellivoice Serial Bus: Serial Input||SER IN||18||17||DB4||Bit 4 of the Address / Data Bus.|
|Intellivoice Serial Bus: External Rom Disable||ROM DISABLE||20||19||DB11||Bit 11 of the Address / Data Bus.|
|Ground||GND||22||21||DB3||Bit 3 of the Address / Data Bus.|
|GND||24||23||DB12||Bit 12 of the Address / Data Bus.|
|GND||26||25||DB13||Bit 13 of the Address / Data Bus.|
|GND||28||27||DB2||Bit 2 of the Address / Data Bus.|
|BUS AcKnowledge.||~BUSAK||30||29||DB14||Bit 14 of the Address / Data Bus.|
|Intellivoice Serial Bus: ROM Clock||ROM CLOCK|
|This is an input. This BC1 drives the EXEC ROMs, the PSG, and the 8-bit RAMs.||BC1||32||31||DB1||Bit 1 of the Address / Data Bus.|
|This is an input. This BC2 drives the EXEC ROMs, the PSG, and the 8-bit RAMs.||BC2||34||33||DB0||Bit 0 of the Address / Data Bus.|
|This is an input. This BDIR drives the EXEC ROMs, the PSG, and the 8-bit RAMs.||BDIR||36||35||DB15||Bit 15 of the Address / Data Bus.|
|This is an output. This BDIR is usually looped back by the cartridge on pin 36.||BDIR||38||37||BDIR||This is an output. This BDIR usually provides the current bus phase to the cartridge ROMs.|
|This is an output. This BC2 is usually looped back by the cartridge on pin 34.||BC2||40||39||BC2||This is an output. This BC2 usually provides the current bus phase to the cartridge ROMs.|
|This is an output. This BC1 is usually looped back by the cartridge on pin 32.||BC1||42||41||BC1||This is an output. This BC1 usually provides the current bus phase to the cartridge ROMs.|
The following meanings are assigned to the cartridge port signals:
- Vcc -- +5v Power
- GND -- Ground
- RESET -- System Reset
Pulling this line low will send a short reset pulse to the STIC. This will result in ~MSYNC being brought low by the STIC, thereby resetting the machine. The signal is capacitively coupled inside the Intellivision. Thus, the Intellivision will only respond to the high-to-low transition of the pulse. Holding this line low will not hold the Intellivision in reset.
- ~MSYNC -- Master Sync
This signal goes low for at least 10ms during Reset. It is generated by the STIC as soon as the STIC recognizes a low pulse on its RESET line.
- MCLK -- Master Clock
This pin provides the 3.579545MHz master clock signal that drives the Master Component.
- BC1, BC2, BDIR -- Bus Control
These are the bus control signals as described in the CPU sections above. The outputs on pins 38, 40, and 42 come directly from the INTAK remapping circuitry. Cartridges generally loop these signals back on pins 36, 34, and 32. The outputs on pins 37, 39, and 41 are also directly connected to the INTAK remapping circuitry, and are the signals that most Mattel cartridges use for determining the bus phase.
It appears the loop-back from pins 38, 40, 42 to pins 36, 34 and 32 exists to allow outside hardware (such as the Keyboard Component) to intercept bus cycles intended for certain hardware inside the Intellivision. For instance, the STIC, PSG, Scratchpad RAM and EXEC ROMs all use the reflected BC1, BC2 and BDIR signals. Only the System RAM uses the unmodified BC1, BC2, and BDIR signals.
It also appears that the reason the Intellivision provides two copies of the outputs for BC1, BC2 and BDIR is to avoid vias on standard cartridges. (Vias are connections between the top and bottom sides of a circuit board.) It is impossible to reflect 3 control lines as standard cartridges do and simultaneously use those lines on the cartridge without at least two vias. Avoiding vias reduces production costs.
The Keyboard Component appears to only provide BC1, BC2 and BDIR on pins 37, 39 and 41.
- DB0 thru DB15 -- Address/Data Bus
This is the 16-bit multiplexed address/data bus.
- ~BUSAK -- BUS AcKnowledge
This signal goes low when the CPU has relinquished the bus during a DMA access by the STIC. It appears possible that external devices can access the PSG, EXEC, and 8-bit RAM during the time ~BUSAK is low, but it's unclear whether this is the case. In all likelihood, it is not the case.
- SR1 -- STIC Timing Signal
This signal is tied to the CPU's ~INTRM input, triggering an interrupt when the STIC goes into the vertical refresh phase.
- CBLNK -- "Character BLaNK" / Horizontal Retrace
Used for genlocking the Keyboard Component's TMS9927 to the Master Component's AY8900 STIC.
- EXT AUDIO -- External Audio Input
The Intellivoice and ECS's second Programmable Sound Generator provide audio input via this pin. I'd imagine if the Keyboard Component can generate Audio, it also provides it on this pin.
- EXT VIDEO -- External Video Input
This was originally designed to accept the genlocked video from the Keyboard Component. The Intellivision II changed the external video input circuit slightly to accept the non-genlocked video from the System Changer. It also moved this to pin 2, which was previously a ground input.
- C1, C2, C3, SER OUT, SER IN, ROM CLOCK, ROM DISABLE -- Intellivoice Speech ROM Expansion Bus
The Intellivoice repurposes several cartridge lines in order to provide its serial expansion bus for speech ROMs. For instance, SR1, CBLNK and ~BUSAK are not available when the Intellivoice is connected, and the System Changer's video input goes to the same pin as "C1".
The signals C1, C2, and C3 provide bus control. SER OUT/SER IN provide paths for moving addresses into ROMs and data back out. ROM DISABLE is an input that apparently disables the external speech ROMs.
No game cartridge seems to have reached production that used this expansion bus.