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Building the XMP1541 Serial+Parallel Y Cable

Parts needed:XMP1541 cable parts

Visit the ports, parts & pinouts page for a descriptions of all the above parts.

Tools needed:

This is called an "multi-task serial-parallel" cable because it not only works under DOS, but also works under multi-tasking OS's like Windows or GNU/Linux using the proper software like OpenCBM. It replaces the X1541 cable in that it is compatible with most present-day parallel ports and their various modes (ECP, EPP) with few exceptions. It is a combination of the XM (serial) and XP (parallel) cables, thus it allows high speed transfers but you must have the C= parallel option installed in your disk drive in order to take advantage of the parallel portion of the cable. It is not a difficult cable to make as it only requires 4 extra Schottky diodes, and has the same pinout as the XA cable. It is almost identical to the XEP1541 cable except two wires are swapped. This cable works with Star Commander and MNIB/NIBTOOLS.

If you're not sure this is the right cable for you, see my cable picking guide to check.

XM cable copyright Michael Klein & Nicolas Welte, 2000
XP cable copyright Joe Forster/STA, 1997

Step 1: Build the diode modules

Just like the resistor/transistor modules for the XA and XAP, this step creates diode/wire-lead modules which are easy to install on the DB25 connector.

Diodes and wires

First, take the four diodes, cut both ends to about 1/2" (1 cm). Make a small loop in the anodes ends (the ones opposite the ends with the circle all the way around). Strip the wires back about 1/8" (1/2 cm), and twist & tin the wires.

Diodes with wires attached

Second, make a loop in one end of each wire, hook it to the loop of one diode and solder the two together. Cut some 3/32" or 1/8" heat shrink tubing to about 1/2" (1 cm), enough length to cover the wire/diode solder joint and just go over the end of the diode. The heat shrink prevents the diode legs from shorting to each other when soldered to the DB25.

Diodes with wires attached

Third, place the heat shrink tubing over the solder joint and the end of the diode and shrink it on. The modules are now ready to be used.

Step 2: Prep the DIN6 plug and attach the wires

Serial wires in DIN6 Wires attached to the DIN plug.

Step 3: Prepare the DB25 connector and attach the diode modules

Step 4: Attach the wires from the DIN6 serial connector

Step 5: Prep the DB15 connector and attach the wires

DB15 parallel wires Wires attached to the DB15

Note that there is no ground line on this half of the cable. This is because the serial half contains the ground lines and an inclusion of a ground line here could cause a ground loop condition, something which must be avoided. Also, the parallel port add-on on the C= disk drive doesn't contain a ground line for this very reason.

Step 6: Prep the other end of the 8 conductor wire and attach to the DB25

DB25 finished The completed DB25 end. Crowded with the diodes in there.

Step 6: Check the cable

Cable pinout chart

DIN6 (male)
DB15 (male)
DB25 (male)
2 (GND)
18-25 (GND)
3 (ATN)
4 (CLK)
5 (DATA)
10 (ACK)
11 (BUSY)
1 (PB0)
2 (DATA0)
2 (PB1)
3 (DATA1)
3 (PB2)
4 (DATA2)
4 (PB3)
5 (DATA3)
5 (PB4)
6 (DATA4)
6 (PB5)
7 (DATA5)
7 (PB6)
8 (DATA6)
8 (PB7)
9 (DATA7)
13 (SELECT) -->|-- 1 (STROBE)
12 (PAPER END) -->|-- 14 (AUTOFEED)
11 (BUSY) -->|-- 17 (SELECTIN)
10 (ACK) -->|-- 16 (INIT)
18 to 25 shorted

Step 7: Finish the cable. Mount the DB ends in their hoods

Finished XMP1541 cable The completed XMP cable

XMP1541 schematic

Schematics drawn using ExpressPCB, a free and excellent solution which also supports PC board layout editing.

Email the author: Peter Schepers | Last updated: June 8, 2009