Lupin's weblog

I wired up a DS1621 digital thermometer IC to the PM. With this IC it’s possible to measure the temperature very easily.

I communicate with the sensor using the same I²C bus functions as for EEPROM access (just one small additional function). The sensor outputs the temperature as 9 bits of data.

The black IC in front is wired to the PM using magnet wire.

My cheap clock/thermometer agrees with the DS1621.

Included in the zip file are instructions to wire up the sensor to the PM, so you can add a temperature sensor to your PM too (and read the temperature if you’ve got a flashcart ).

I wrote some I²C functions for the PM, they can be used to access the savestate EEPROM. The functions should be quite easy to use. I uploaded a sample of writing a few bytes to the EEPROM and reading them back. You can find it in the PM section.

PlayerOne discovered how to read from the EEPROM, the website of the Embedded Systems Academy had some useful informations to implement the functions like it’s specified by the I²C protocol.

Download the example.

I used the Pulse-Width-Modulator of the PMs sound generator to play real wave samples. By changing the duty of the output wave it is possible to “emulate” an analog sound signal. The output sounds quite good, but the PM is not loud enough so it’s a good idea to hold your PM close while testing these ROMs.

I noticed that 8 bit samples sound more awfull then 6 bit samples, in this version you can use the B button to decrease the bit-width of the samples down to 5 bit (i think 6 bit sounds best) and the A button to increase it again (up to 8 bit of course). This problem probably occours because the lower the bit-width of each sample the higher the PWM units frequency (which in turn results in a better signal quality).

Here’s the link to the sample binaries and source.

I changed one of my tutorials so that it displays an image without actually using the PMs drawing circuit. The PM offers two hardware registers – 0xFF and 0xFE – to access the LCD controller directly, this gives us the opportunity to send whatever we want to the display controller.

I figured out some commands of the controller using this datasheet which i found on darkfaders website, but not all commands in the datasheet seem to work or the PM hardware interferes when you try to use them.

The PM drawing circuit does exactly the same as my code, but it doesn’t draw directly to GDDRAM, instead it first draws to the frame buffer at 0×1000 and while the LCD is in VBLANK it copies the framebuffer over to the LCD controller GDDRAM. Of course writing the GDDRAM yourself saves some RAM since you don’t have to use the framebuffer but it is slow and you have to draw everything yourself.

Download the source+binary here – this will, of course, only work on real hardware.

yay! It looks great and works like a treat!