P112 Mounting considerations



  The P112 is designed to mount directly to the bottom of a standard 3.5” floppy drive.  When the GIDE board is added, there probably will not be enough room for both boards, so consideration will have to be given to mounting the P112 separately.  Additionally, the P112 kit is supplied with a vertical mount holder for the 2032 coin cell battery.  This battery holder is too tall, and will have to be relocated.  It’s possible to remove the battery holder and mount it flat to the P112, or you can use an external battery.


  Another possibility is to mount the P112’s 48-pin expansion connector to the bottom of the P112, rather than the top.  This will put the GIDE under the P112, and the battery holder can remain as is.  This method prevents the addition of a second expansion board to the 'stack,' but the GIDE's 50-pin expansion header will allow future expansion.  Standoffs and connector pins for this mounting method are not supplied.


  The GIDE kit contains two sets of standoffs.  Four 3/8” M-F standoffs are used to mount the P112 to the cabinet, and four 3/4” M-F standoffs are used to mount the GIDE to the P112.  The standoffs are made of aluminum, and WILL shear off if you over-tighten them!


  Determine how and where the P112 will mount in the cabinet, and mark the locations of the mounting holes.  Drill the holes and verify correct alignment, but don’t install the 3/8” standoffs yet.



GIDE Assembly


  Use the schematic and PCB layout diagrams to ensure correct placement of parts.  PCB orientation is with the 3x16 expansion connector to your right, and the 2x20 IDE connector to your left.  The large ground and power buses are on the bottom of the board and should be facing down.


1.  Install sockets for IC1-IC4.  If desired, obtain and install an 8-pin socket for SW-1 (see step 8.)


2.  Install four .1ufd monolithic capacitors at the top of U1-U4.  Polarity does not matter.  Clip excess leads.


3.  Install R1 and R2, 330 ohm resistors.  Clip the excess leads.


4.  Install RN1, the 10K, 6-pin resistor pack.  Pin 1 (with a stripe or dot) goes to the top of the board.


5.  Install IDS1 – the 2x20 pin, IDE header.  Note that pin 1 is at the top left.  This can be tricky and, if done wrong, can make it nearly impossible to attach the IDE cable.  Take a look at your IDE cable.  Oftentimes, the connector is ‘keyed’ such that it can only plug in one way.  This can take two different forms: 1) the key might be a raised area on the connector body that aligns with a notch in the corresponding socket, or 2) pin 20 of the connector might be filled, requiring the corresponding pin on the male connector to be removed.  Occasionally, both methods are used.  However, the P112-GIDE adapter uses neither.  Insert the right angle header in the appropriate connector on your IDE cable, paying attention to pin 1 (usually marked with a red wire on the ribbon cable), and insert the header into the GIDE with pin one towards the top of the board.  If your cable connector has the raised area key, it will be facing down, towards the top of the board, and will prevent the right angle header from seating against the PCB properly.  In this case, the key will have to be removed by shaving, sanding, or grinding.  BE CAREFUL!  Don’t damage the ribbon cable!


6.  Install D1, the HD Activity LED.  The flat edge at the base of the LED goes toward the top edge of the PCB.  Clip the excess leads.


7.  Install J1, the 2-pin header for the External HD Activity LED connection.


8.  The jumper straps at SW-1 are used to determine the base address of the GIDE controller.  For the P112, the port should normally be hardwired to address 50H.  This can be accomplished by using the excess lead lengths from R1 and R2 to install jumper straps.  SW-1 provides the high order 4 bits of the base address.  Each bit is tied HIGH via separate pins of RN1.  Inserting a jumper strap will ground the bit, providing a ‘0’.  So SW-1, from left-to-right, bits 7, 6, 5, and 4, would normally be 50H -> 0101 -> Strap, no strap, strap, no strap.


An alternate method would be to use a 4-position switch in place of the straps, allowing flexibility of base address.  Note that the B/P BIOS (supplied with this kit) expects the base address to be 50H.  If you choose to go this route, you’ll need to obtain the 4-position DIP switch and socket separately.


9.  Before installing the 3x16 expansion headers, mount the GIDE to the P112 using the supplied 3/4” standoffs and 6-32 screws and nuts.  This is necessary to ensure the correct alignment of the expansion headers.  The expansion headers are supplied in a 1x30 pin format.  Each GIDE board requires 48 pins in three, 1x16 rows, so the headers will have to be cut to fit.  They are designed as ‘snap-to-size’ headers, but even so, be gentle with them.


CAUTION: There is very little room to work here, and the traces are quite close together.  A little too much solder can make the board (or your P112) inoperable!


Insert the ‘A’ row (furthest from the card edge) of 1x16 pins into the top of the GIDE board and down into the ‘A’ row of the P112 expansion connector.  The pins should seat all the way into the expansion connector.  Ensure the pins stay seated and solder the ‘A’ row of pins in place from the bottom of the GIDE board.  It's very tight in there.  Take your time, do it right, and don't get sloppy with the solder!  Do the same with the ‘B’ row, and finish with the ‘C’ row.


10.  Disassemble the two boards.  Using 6-32 nuts, install the 3/8” standoffs in the P112’s cabinet, and use the male side of the ¾” standoffs to mount the P112 to the 3/8” standoffs.  These standoffs are aluminum - don't 'horse down' on them!


11.   Install the ICs in their sockets on the GIDE.


U1  - GAL20V8

U2  - GAL16V8

U3, U4 - 74F646 (or 74ABT646)


  Finally, install the GIDE on top of the P112 using 6-32 screws.  Ensure the expansion connector is lined up properly, then press it in place and install the screws.



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