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Building the XAP1541 Serial+Parallel Y Cable

Parts needed:XAP1541 cable parts

*Note: in the above parts picture there are 4 small black parts beneath the DB25 connector. These are the BSV52 transistors, and yes they are that small! Visit the ports, parts & pinouts page for a descriptions of all the above parts.

Tools needed:

This cable is called an "active serial-parallel" cable because it uses active components like transistors (and resistors), but these components also make it the most difficult to build. It is a combination of the XA (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. This cable has the same pinouts as the XMP1541, and works under DOS, but it is also a multi-task cable and works under multi-tasking OS's like Windows or GNU/Linux using the proper software like OpenCBM. It is also the most compatible cable with present day parallel ports and modes, and is designed to work where the X, XE and XM cables fail. The XA cable requires inverted logic to drive it compared to the other cables due to the use of transistors. 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.

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

Step 1: Build the transistor/resistor modules

This is the hardest step simply because of the small size of the surface mount transistors being used. You will need magnifiers or have really good eyes to work with these, and they are very easy to lose! It is also very easy to confuse the base and emitter legs because the transistor looks very similar from the bottom and top. The bottom is where the legs bend down towards.

The following construction process may seem complicated but once you build a few of the modules it becomes much easier. The lengths of the lead wires are critical to making this work well because if they are too short then the modules start getting stressed. If this procedure seems too daunting, then I strongly recommend you buy a cable instead.

BSV52 size comparison BSV52 with wires attached Completed BSV52 module
For a size comparison, the screw is a standard computer case screw. The completed module, without heat shrink. The completed module, with heat shrink, and a ruler to see the measurements.

Step 2: Prep the DIN6 plug and attach the wires

Serial wires on DIN6 DIN6 finished
Wires attached to the DIN plug The completed DIN6 end

Step 3: Solder the transistor/resistor modules to the DB25

Modules getting soldered Modules soldered
The modules are partially done.. The modules are all soldered.

Step 4: Prep the DB25 connector and attach the DIN6 wires

DB25 solder bridge DB25 serial wires
The solder bridge on the DB25 from pins 18 to 25. The DIN6 wires are attached.

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 completed
The completed DB25 end. Crowded with the modules in there.

Step 7: Check the cable

Cable pinout chart

DIN6 (male)
DB15 (male)
DB25 (male)
2 (GND)
18 to 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)
18 to 25 shorted

The four transistor/resistor modules in the DB25 are attached like this:

Module 1: resistor lead to pin 1, red wire to pin 13, black wire to ground strip (solder bridge on pins 18 to 25)
Module 2: resistor lead to pin 14, red wire to pin 12, black wire to ground strip (solder bridge on pins 18 to 25)
Module 3: resistor lead to pin 16, red wire to pin 10, black wire to ground strip (solder bridge on pins 18 to 25)
Module 4: resistor lead to pin 17, red wire to pin 11, black wire to ground strip (solder bridge on pins 18 to 25)

Step 8: Finish the cable. Mount the DB ends in their hoods

DB25 in hood Finished XAP1541 cable
Fitting the DB25 into the hood. The completed XAP cable.

XAP1541 schematics

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

Email the author: Peter Schepers | Last updated: Mar 17, 2009