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Category Archives: avr

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XMEGA USART unsets output direction on ports when disabling TX

02/02/2012 – 15:23

I noticed that if I set the TX pin of a port to output and then enable the USART it works. If I then disable the TXEN bit (necessary because with IR comms the TX line has to be held low during reception, otherwise the transceiver blinds itself) the TX port pin is reset to being an [...]

By mojo | Comments (0)

RFM12B bit stream sync issue

22/12/2011 – 16:04

Been working with cheap RFM12B modules at work and discovered something interesting about them. A couple of things actually, the first of which is that the datasheet for the Si4420 IC it uses is much better. The main issue is that the serial data stream you get when receiving is not always aligned to the [...]

By mojo | Also posted in electronics | Comments (0)

Compile time asserts in C

21/12/2011 – 15:48

Assert is a useful function that checks a condition and outputs an error if it is not met at run time. Aside from generating some overhead in the code it is also pretty useless on microcontrollers because the messages go to STDERR and, well, there isn’t one. A much better solution is to do the [...]

By mojo | Comments (0)

XMEGA TWI (I2C) bus pull-ups

24/11/2011 – 16:32

The XMEGA 128A1 and XPLAINED hardware guide both suggest that TWI should work with the internal port pull-up resistors. Those pull ups are 50K+ and don’t pull enough for most devices. In short external pull-ups, say 10K, are essential.

By mojo | Also posted in electronics | Comments (0)

Using the XMEGA DMA controller

04/11/2011 – 11:47

Finally got the XMEGA DMA controller on an ATxmega128A3 working. There is not much example code for it and the datasheet is not very clear, so I wrote this. The datasheet and examples don’t really explain the terminology well. A transaction is the complete cycle of the DMA controller. To start a transaction you load [...]

By mojo | Also posted in electronics | Comments (0)

The MSF signal is a bit of a mess

28/07/2010 – 00:06

I am working on another clock, this time with MSF (Rugby/The time from NPL)  radio time setting. I know, I need to document the last one… Anyway, I finished the decoder today. The MSF signal is frankly a mess. Things seem to have been added and then removed over the years. There are four different [...]

By mojo | Also posted in electronics, microcontrollers | Comments (0)

AVR / electronics quick reference sheet

23/04/2010 – 18:31

I am working on a quick reference chart (cheat sheet). It’s by no means done but a post over at Adafruit made me think to post it: quickref.pdf

By mojo | Also posted in electronics | Comments (0)

Playstation controller protocol quirks

22/02/2010 – 01:29

Today I discovered why I have been having a few compatibility problems with my Playstation interface code. The PSX uses a SPI bus. The device is supposed to put data on the bus when there is a high to low transition, then read the command on the low to high change. Sure enough the official [...]

By mojo | Also posted in electronics, microcontrollers | Comments (9)

2nd DB9 Connector in the works

25/10/2009 – 19:24

I am doing the code for a 2nd DB9 Connector for the Retro Adapter. It converts the DB15 into another DB9 so you can connect two controllers simultaneously for 2 players. Atari/Commodore/Sega controllers are working and I will add support for NES and SNES too. I will probably do N64 as well. The button mapping [...]

By mojo | Also posted in electronics, Retro Adapter | Comments (0)

Retro Adapter on sale soon and Retro Adapter Wii

06/09/2009 – 17:45

I will be opening the online shop for sales of the Retro Adapter soon (just waiting for the final parts to come in). Both finished adapters and kits will be available, as well as  a selection of connectors. It occurred to me that I can use the same PCB for a Wii/Gamecube version, so I [...]

By mojo | Also posted in electronics, hardware | Comments (0)
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