The subject line of this post could have been also: Using the 8052.com SBC with AT89S52.

As I happened to have one around, I decided to try it (to be honest, so far I never tried the AT89S8252/8253, which is the "default" processor of the 8052.com SBC).

I downloaded and fired the programming utility for the SBC, to find out that it supports only the '8252/8253. OK, what now.

I do have ways how to program the 'S5x, but considered that a cheating. There must be way how to do it via the parallel port - after all the discussion about how crappy that way is, I wanted to try it for real.

I chose Adam Dybkowski's ISP Programmer, as it allows to almost freely chose the pins on LPT connector for the individual ISP signals. However, it also presents one problem - the SELECT signal, which is an enable signal for the buffer, has a different polarity than the 74HC126 at this position would require (the software allows to choose polarity of RESET signal, but unfortunately no other signals).

That's no tragedy as the 74HC125 has identical pinout to the '126 and has different enable signal polarity. Problem solved? Partially. As long as the connector stays connected and the ISP Programmer is running, everything is OK. But beware: removing the connector would block the board, thanks to the pulldown R6 (which is logical when the enable-active-high '126 is used); and so would do restart of the PC. So, this might require a fix - I'd consider a jumper and a pulldown - maybe I will "steal" it from the serial ISP circuit.

OK so with 'HC125 in place of 'HC126, let's play with the ISP Programmer's setup:


One more word of caution, there must be NOTHING connected on the - the LCD module I have used pulls down the MISO pin enough so that the internal pullup of 'S52 could not push it through (and there are no external pullups on the board).

Now, on the main window, pressing Read Signature should return the valid signature for the AT89S5x, and the appropriate set of buttons should light. Since here the rest of programming is a piece of cake... :-) After programming is finished, Reset OFF should be pressed to start the program.

It took some experimentation, but then I was surprised how smoothly it went. Of course, it does not mean it will work with every combination of LPT port and cable, but at least the problem of long ISP cable (after the buffer) is not present here.\

I hope this will be of some help.

JW