A simple way to export the NABU's option card to via a common DB interface. Almost all pins map exactly from the NABU Option Card specification to the DB-25 pins, with the exception of the power pins. The ENID is meant to take the place of a NABU Option Card Plate. Each NABU has 4 removable metal plates to allow for external interface and access to any Option Cards installed. These plates correspond to 4 30-pin Option Card interface mounted on the board.
I wanted to extend the abilities of the NABU. The most convenient way of doing this without disrupting the main system is to make use of the Option Card bus -- a series of 4 30-pin connectors on the motherboard that allow for the addition of peripherals and hardware extensions. My issues:
- I want to keep internal access to a minimum -- ideally, connect up to all 4 slots to ENIDS, then button up the NABU.
- I do not want to cut into the Option Card Plates -- leaving them intact, as the NABU is a collectible item with limited parts availability.
- I want to add protection by both limiting the exposed power access to a fusable 5V rail, and keeping the +12V and -12V rails disconnected.
- I want a widely adopted interface connector. DB-25 is very popular for legacy serial and parallel PC interfacing, and cheaply available on electronics supply sites.
- BEAVER Boarduino Adaptor to allow for testing and peripheral prototyping.
- PC Gameport -- TBA - To support Gameport joystick and peripheral input.
- RC2014 adaptor -- TBA - To support [RC2014] (https://rc2014.co.uk) peripherals.
The DB-25 is a 25-pin interface, used in many applications, primarily RS-232 serial and PC parallel cabling. When selecting a cable or connector, care should be taken to select one where all pins are connected -- some serial cables may have only a few pins connected (RX/TX, DTS/RTS, etc).
Since the DB-25 connector has 5 less signals available than the NABU Option Card interface exposes, the following are not propagated:
- +5V rail 2
- Ground rails 2 & 3
- +12V rail
- -12V rail
As well, ground rail 1 is redirected from NABU pin 26 to DB-25 pin 25, as per the Pinout table.
The connected +5V rail can be connected either directly (not recommended) or connected to a fuse with a 1x2 electrical jumper. The specifications call for a ~1A resettable LittleFuse-brand fuse, but other fuses can be used, if their leads fit in themsoldering holes.
- Ensure that the cable used is not a null-cable or loopback-cable. You can tell if pin 2 (RS-232 Receive) and pin 3 (RS-232 Transmit) are switched at each end using a multimeter.
- Connecting and disconnecting the DB-25 cable exerts a considerable force on the ENID. It is recommended to add a non-conductive reinforcement across the 2 Option Card Plate bolts.
- The 2 1x13 connectors on the ENID card (JOP1 & JOP2) should be male, as the card is receiving power. JFUSE1 (1x3) should also be male to accommodate a jumper to select the power mode.
- The BOM calls for 2 1x13 0.1"(2.56mm)-pitch cables, female on both ends.
- The existing Option Card plate screws will not suffice to hold the ENID card in. Upgrade to a pair of fitting bolts and nuts.
- The PCB is connected to the NABU as a plate by 2 bolts. Use of this involves plugging in a DB-25 connector, which exerts a considerable force on the board. I highly recommend sandwiching the PCB with a nonconductive backing material behind it, on the same bolts, to take the strain of the plugging. I also recommend providing counterstrain to the female DB-25's tabs when plugging a male DB-25 connector in.
- This is NOT a direct parallel or serial interface. Trying to connect devices as such won't work without an intermediary device, and may harm your NABU, external device, or self-esteem.
- Mind how you plug the 1x13 Connectors into the Options Card pins. They plug into pins 1-13 and 14-26. 27-30 should not be connected. Especially considering that Pins 29 & 30 may be +12 and -12 volts respectively. I'll add pictures and video once I start adding boards. NABU Option Card pin 1 appears to be the furthest back in the NABU enclosure.
ENID's pinout should map almost exactly to the Option Card pinout, with the exception of the first ground rail NABU pin 26, which on the ENID is pin 25; and of course, NABU pins 25 & 27-30 are not propagated.
| ENID DB-25 | Input from NABU | Description |
|---|---|---|
| 1 | 1 | Interrupt |
| 2 | 2 | Interrupt Acknowledge |
| 3 | 3 | 3.58 MHz Clock |
| 4 | 4 | Audio |
| 5 | 5 | Chip Select |
| 6 | 6 | Address 0 |
| 7 | 7 | Address 1 |
| 8 | 8 | Address 2 |
| 9 | 9 | Address 3 |
| 10 | 10 | 1.79 MHz Clock |
| 11 | 11 | Write |
| 12 | 12 | Read |
| 13 | 13 | I/O Request |
| 14 | 14 | Wait |
| 15 | 15 | Reset |
| 16 | 16 | Data 0 |
| 17 | 17 | Data 1 |
| 18 | 18 | Data 2 |
| 19 | 19 | Data 3 |
| 20 | 20 | Data 4 |
| 21 | 21 | Data 5 |
| 22 | 22 | Data 6 |
| 23 | 23 | Data 7 |
| 24 | 24 | +5V Rail 1 |
| 25 | 26 | Ground Rail 1 |
| Input from NABU | Description |
|---|---|
| 25 | +5V Rail 2 |
| 27 | Ground Rail 2 |
| 28 | Ground Rail 3 |
| 29 | +12V Rail |
| 30 | -12V Rail |
- The board is anchored to the NABU box by 2 bolts. There is no reinforcement for the RS-232 connector. There is a concern that over time the stress of plugging & unplugging the connector will cause the PCB to crack from the forces required. PCBs ordered should have a composition and thickness as high as can be reasonably ordered (don't cheap out). Alternatively, a non-conducting reinforcement bar can be layered behind the PCB, connecting to the aforementioned bolts, but able to absorb the strain imparted by connecting a DB-25 connector.
- The DB-25 connector, in general, is used in serial and parallel applications. None are compatible with ENID. Attempting to connect this to a serial or parallel device will very possibly cause some magic smoke to spew out. However, this is designed to be a springboard to add adapters to connect to various devices using new or existing PCBs or microcontrollers.