DIY prototype RPN/TENKEY programmable calc with printer <:3)--

[macieksoft]

(07-08-2020 06:18 AM)grsbanks Wrote:  It only operates at 400KHz, so like you, I had to slow my I²C bus down so that the chip could keep up with it.

I am using 4 bit parallel communications for LCD (not I2C). Both LCDs goes on same bus, that means data pins and RS pins are tied together, and only the E (enable) pins are separate. The left LCD is taken from cash register, right one is left over from previous projects.

EDIT: Got VGA working. I used EP2C5T144 FPGA and used Grant's Multicomp project. It is essentially a modular retrocomputer on FPGA, but it has all i needed. Just needed to replace ROM for Z-80 soft core to turn in into terminal. Now i got the big screen. VGA terminal may be used as extra screen (with it's own display mode selection independent of LCD alphanumeric displays), or it can be used as virtual printer when it behaves like regular printer. It supports 3 bit colors (can be expanded to 6 bit by adding extra resistors).
I have also fixed some funky bug related with printing that was causing a string variable to grow bigger and bigger each time i used print function, it was eventually causing calculator to hang.