Re: Frankenstein UART Board #Serial #Homebrew

Martin Heermance

Wow! I love it.

Don't sneeze or a wire might get knocked loose and finding which one would be a heck of a challenge.

On Thu, Oct 3, 2019 at 12:09 AM Jeff Truck <jeff.truck@...> wrote:
Another creation.   Uses the 1854 UART in Mode 1.   IO Group 02.  

OUT4: configure interval counter
OUT5: set interval counter initial count.  
OUT7: set UART control register. 
IN7: read UART status register.  
OUT6: send byte.  
IN6: receive byte.  

/EF2 is /DA
/EF3 is /THRE

Uses a 3.6864 MHz oscillator to derive baud rates of 300,1200,2400,4800,9600,14400,19200,28800,38400,57600,115200.  I have tested the 115200 but at that speed with Frankie running at 4MHz I had to add some delay in the program to prevent overrun.  

Very fun to build.   

2k EEPROM programmed to control the UART and the programmable interval timer control lines.  A 74HC138 decodes the N lines to set one of six utilized ports as an address to the EEPROM.    The 82C54 is in itself an interesting little chip.  I use mode 3.  

The 1854 can be found at Jameco.   Mine is date stamped 745.  

Yes I cheated slightly by using a FTDI chip for USB connection to my home computer.  It is connected to TX RX /CTS and /RTS on the 1854.  

Frankie’s main board IO for data display, keypad and video on/off was converted over to IO GROUP 01.  


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