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Internal Serial Port
MP2x00 devices have an internal serial port connector. The official purpose is a connection to an optional internal modem. The case has a cutout in the back to fit a telephone jack.
A document named "Internal Serial Slot Designer's Guide" made it into the archives and gives very nice insight into the many capabilities of this port. Note however, that the document was not finalized and does contain errors. Information on this page is based on actual measurements and existing deices.
To access the port, the back of the MP2x00 case must be removed. There are a few square centimeters of space in the case that can be used for a small (1994), or huge (2024) PCB, holding a modem and other things. The header on the main board is a JAE IL-WX-32PB, the receptacle on the modem is a JAE IL-WX-32SB. These connectors are no longer made, but can be found with a bit of luck.
The port has 32 pins. Pin 1 is at the to right when looking at the modem (or top left when looking at the bottom of the MP2x00 PCB):
| Function | Name | # | # | Name | Function | ||
|---|---|---|---|---|---|---|---|
| Modem Ring Indicator | ModemRI | > | 17 | 1 | > | PortSelect | internal modem card may use modem port |
| Modem Transmit Data | ModemTX | < | 18 | 2 | > | SCCTX0 | serial port 0 transmit data |
| Modem Receive Data | ModemRX | > | 19 | 3 | > | SCCNotDTR | Ser0 Data Terminal Ready |
| Modem Ready To Send | ModemNotRTS | < | 20 | 4 | > | SCCNotRTS | Ser0 Ready To Send |
| Modem Clear To Send | ModemNotCTS | > | 21 | 5 | < | SCCNotDCD | Ser0 Data Carrier Detect |
| Modem Data Terminal Ready | ModemNotDTR | < | 22 | 6 | < | SCCNotCTS | Set0 Clear To Send |
| Modem Data Carrier Detect | ModeNotDCD | > | 23 | 7 | < | SCCRX0 | Ser0 receive data |
Keyboard Serial Transmit, internally name tblt
|
KeyBdTX | < | 24 | 8 | > | gpSerPortSel | switch serial port 1 between interconnect port and internal port |
| Keyboard Serial Receive | KeyBdRX | > | 25 | 9 | > | PowerEnable | set if running |
| General Purpose I/O | GPIO | <> | 26 | 10 | < | PsAdptIn | Power Adapter Installed |
| 12V, software controlled | D12DCC | < | 27 | 11 | > | D5VCC | 5V, software controlled |
| Sound Input | SoundIn | > | 28 | 12 | > | DVCC | 3.2V permanent |
| Ground | GND | ⏚ | 29 | 13 | <> | UnFusedPSVIn | 7.5V |
| Ground | GND | ⏚ | 30 | 14 | <> | UnFusedPSVIn | 7.5V |
| Ground | GND | ⏚ | 31 | 15 | <> | UnFusedPSVIn | 7.5V |
| Ground | GND | ⏚ | 32 | 16 | <> | UnFusedPSVIn | 7.5V |
- SCCTX0 : transmit data from the MP to the modem card
- SCCNotDTR : set to 0V when the MP is ready to receive data
- SCCNotRTS : 0V if ready to receive data, 3.2V if other side must suspend sending data
- SCCNotDCD : card should set this to 0V if it can receive data
- SCCNotCTS : card should set this to 0V if it can receive data
- SCCRX0 : MP receives data from the card via this line (8N1 by default)
- KeyBdTX : send data from the MP to the card wich may connect to a keyboard. This line sends an ESC byte after the boot sequence at 10kbps. That's all we know so far.
- ModemTX : transmit data, 8N1, LSB first. Note that selecting "Modem" in "Dock" alone will assume an external modem connected to the Interconnect Port. To use the internal port, the user must set the mode port in the preferences app.
- ModemRX : 8N1, receiving means that the MP receives data from the internal modem
- ModemNotRTS : 0V if MP is ready to receive data, 3.2V if other side must suspend sending data
- ModemNotCTS : modem card should set this to 0V if it can receive data
- ModemNotDTR : 0V if MP is ready, 3.2V if MP is busy
- ModeNotDCD : modem card should set this to 0V if it can receive data
- PortSelect : documentation says, when 0V, the interconnect port connects to serial 3 (modem), and when 3.2V, the internal modem may drive the port. This needs to be verified!
- gpSerPortSel : There is a short pulse during boot? (Verify). This seems to go to 3.2V while Dock is using the serial port (verify).
- PowerEnable : 0V when in sleep state, 3.2V when idle or running
- PsAdptIn : if the board has a power input that can supply power to the MP or even charge it, this pin needs to be connected through a current limiting resistor to 10mA (how about 1kOhm?).
- D12DCC : 12V with very little power.
- D5DCC : software controlled 5V power, on when Dock opens
- SoundIn : probably 0..1V audio input, meant to play the carrier during modem connect?
- UnFusedPSVIn : Directly (?) connected to the battery, or 7V from the power supply if no battery is installed