uTasker uTasker

uSD-card of LCD extension board

Discussion created by uTasker uTasker on Sep 24, 2010
Latest reply on Nov 26, 2010 by uTasker uTasker
Hi All

I have just received an LCD extension board (TWRLCD) to go with my M52259 tower kit.

First of all I adapted my graphics driver to suit the LCD via 16 bit FlexBus and this was OK.

As second step I added my SD-Card driver so that I could display images from it to the LCD (slide show). This second step didn't work at first and involved soldering wires to the underside of the board, directly to the SD card socket so that it was possible to see what could be going on (due to lack of test points in this area).

The signals did seem OK, up to the uSD-MISO line which was always low '0'. so I soldered in a pull up resistor directly to the SD card socket so that it would be pulled up (the pull up in the M52259 doesn't help since there is a 74LCX244 in between so that the on-board MCF51JM128 can control it and isolate the tower circuitry.

The next problem was that the signal going back to the M52259 was only about 1V rather than 3V3. There was obviously something driving the line and after some hunting I could see that it was coming from the second half of the same 74LCX244 which was isolating the SPI mode of the LCD.

If I switched the SW1 DIP switch 3 off so that this was not driving the SD card finally worked correctly. But, this also caused the LCD to stop working in 16 bit Flex-Bus mode...

So I cut the track to back-plane B44 on the M52259 processor board so that the signal ELE_MISO from the LCD extension board was no longer being 'shorted' with the MISO line from the SD card (allowing DIP 3 to be left ON) and then the slide show finally operated correctly. That is, SD-card working via QSPI and the LCD operating via 16-bit Flex-Bus.

The question is, why do I have to break tracks on the processor board? Is the system not designed to run the SD-card together with LCD from the M52259? Or is there a better solution? Is it necessary to add the pull-up resistor (without it I didn't seem to get any output from the SD card).