184-028   IBM Portable PC 5155 Model 68 

5155 Planar
   SW1 System DIP Switch
   5155 Origins
   640K Hack
   Planar Memory Error Codes

5155 Planar
C1 Color trimmer capacitor
E1Solder pads for two pin header
E2 Pads for four pin header
E3 Pads for eight oin header
E4 Pads for four pin header
E5 Pads for three pin header
J1-8 8 bit ISA slots
P1,2 Power conn
P3 Speaker
SW1 System DIP Switch
U3 8088
U4 Socket for 8087
U18 MK38036N-25
U19 AM9265DPC34567
U25 8295A
U26 8253-5
U28 8237A-5 Bios/Basic
U29 8255A-5 ROM
U84 empty 16 pin DIP socket
Y1 14.318 xtal

SW1 System DIP Switch

1 POST Mode     ON       Continuous loop for diagnostic use
                OFF      Normal Operation
2 Math Co       ON       8087 Not Installed
                OFF      8087 Installed (Seems wrong, but...)
3,4 Planar Mem 
                ON/ON    1 Bank  (64K)
                OFF/ON   2 Banks (128K)
                ON/OFF   3 Banks (192K)
                OFF/OFF  4 Banks (256k)
5,6 Display Attatched
                ON/ON    EGA,VGA
                OFF/ON   CGA (40x25 Color) 
                ON/OFF   CGA (80x25 Color)
                OFF/OFF  Monochrome

7,8 Diskette
                ON/ON    1 Floppy Installed
                OFF/ON   2 Floppies Installed
                ON/OFF   3 Floppies Installed
                OFF/OFF  4 Floppies Installed

5155 Origins
Rick Ekblaw wrote:
   The 5155, called the PC Portable by IBM but usually called the "Luggable" by everyone else, was basically a PC/XT with a small, built-in amber composite monitor (driven by a standard CGA adapter), so you could use the PC/XT Advanced Diagnostics on it.  Lots of folks put a half-high hard drive in it instead of a second floppy drive, the Seagate ST-225 was commonly used for the task (or the ST-238R if you opted for an RLL hard drive controller).  The 5155 power supply
provided only 114 watts instead of the 5160's 130 watt supply, so you didn't want the hard drive drawing too much power.

640K Hack
Gfretwell wrote:
  The XT supports 640k and with the addition of one chip 74LS158 in u84 (plug in) and a jumper it will support 640kb on the system board with 2 banks of 256 chips and 2 banks of 64s. Weee! It was still a handy trick for saving slots. You can also plug in a 5162 (286) board with no  modifications. A handy 5155 "luggable" trick

Bob Eager sez:

> Which jumper?

Looking from the front, about halfway back on the right edge of the planar. There are two sets of pads, and the pair you need should be labelled pads 1 and 2 on E2. Jumper those, either with a wire bridge or a proper jumper block.

Then put a 74LS158 into the empty socket near front centre (U84) and replace memory banks 2 and 3 (which normally take 4164 (64K chips)) with 41256-15 chips. Make sure switches 3 and 4 are OFF on DIP switch bank SW1.

Access is a problem as the FDD bracket gets in the way of both operations. Since I wanted to put a removable jumper block at E2 (so I could back out the mod. if necessary) I just took the entire planar out!

> What did the reset switch attatch to?

   Ground and one of the pins on the 8284 clock/reset chip (rear, near right hand side looking from front, near the keyboard socket). Probably should have used a resistor but didn't. The chip is socketed so I used solid core, thin wire, removed chip from socket, poked wires into socket and put the chip back! Pin 9 is gound, and pin 11 is reset input (active low).

5155 Planar Memory Error Codes

Memory failures are displayed as a 7 character code followed by a 201. If the first digit is 0, 1, 2, 3 then it's a planar memory failure.0,1,2,3 indicates the bank with the memory failure. Digits 6 and 7 show the failing module.

Sixth and seventh characters
00  01  02  04  08  10  20  40  80
P   0   1   2   3   4   5   6   7

Example - 3C000 40 201
            |    |  |
Bank 3 -----|    |  |---- Memory Failure
            Failing Bit

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