I use a device that monitors communications and outputs the signals and levels to a parallel LCD. I'd like to be able to log to SD what is displayed on the LCD along with the date and time. The person who designed the device isn't willing to give a serial data output for this purpose. So, in short, is it possible to decode parallel data going to a LCD?
Decode parallel data going to a LCD
- Thread starter lewisg
- Start date
hippy
Ex-Staff (retired)
Yes, but whether that is achievable with a PICAXE alone is a different matter. You need to latch the data and other control lines every time E goes high and then work out what the sequence of data means. Bursts of E pulses may be as short as 1us long and just 40us apart.
westaust55
Moderator
westaust55
Moderator
hippy cloned his own words faster than I . . . . . 
You guys are quick...
In general does E go high once per character or once per line or screen. The text on the LCD only updates once every several seconds. Text only, all caps, no extended characters or graphics. Hex 20 - 5A.
westaust55
Moderator
Assuming a Hitachi HD44780 (or clone) LCD controller, a look at the datasheet explains a lot of this sort of informatio0n.
See: https://www.adafruit.com/datasheets/HD44780.pdf
Page 22 fig 9 for the 4-bit interface. Note one E pulse per data (nybble = 4-bit) transfer
See: https://www.adafruit.com/datasheets/HD44780.pdf
Page 22 fig 9 for the 4-bit interface. Note one E pulse per data (nybble = 4-bit) transfer
The pinout is in the one page datasheet. You don't need a full datasheet since HD44780-compatible LCDs use standards unlike serial LCDs which could use anything.
All HD44780-compatible LCDs allow you to read from them so you can 'take control' of it by using a digital bus switch, read the data from it, then return control to the whatever-it-is. You should set the address to something outside of the display range after reading from the LCD so that if the device was starting to send data to the LCD when you took control of it, text won't briefly appear in the wrong place when you return control.
westaust55
Moderator
Not all LCD displays use the Hitachi controller. Some use the KS0066U controller chip.
I salvaged some Hantronics displays which used the KS0066U chip. See this thread where I got mine working:
http://www.picaxeforum.co.uk/showthread.php?23589-Hantronix-LCDs-Specifically-HDM20416L-1-and-similar-with-KS0066U-controller-chip