A failed experimental attempt of building something like a 6551
with 74XX TTL chips.
Most things are untested, the schematics are a mess,
and there is no documentation.
Failed to get the 2R51 receiver working at all.
I'm not sure, if my concept for the receiver was the right approach.
Decided, that it's better not to include that receiver
into the project files, to prevent people from following me
an a track which probably might be wrong.
If you made it to build a working receiver,
please post the schematics.
Test setup:
Bottom: my DRC2 SBC, which is supposed to be compatible to the SBC-2.
2B22 bus interface is plugged into DRC2.
1X51 backplane is plugged into the 2B22 bus interface.
Plugged into the 1X51 backplane, we have:
1* 1C51, control module
1* 2F51, flag and status module
1* 2R51, receiver module
1* 2T51, transmitter module
1* G51, baud rate generator module
1* D51, RS232 level converter module
1X51 backplane:
This module is used in the X50 and X51 project.
Because register addresses for both projects are different,
we have to compensate this with a few jumpers in the left upper area
of the PCB.
Also, there is a three pin jumper for connecting the interupt output
either with NMI or IRQ.
The jumper in the right lower area enables the blinkenlights.
D51 RS232 level converter module
RS232 to TTL and back level converter.
Concept and jumper field are stolen from Daryl's SBC-2.
This module is used in the X50 and X51 project.
G51 baud rate generator module
All those odd 6551 baud rates...
The 100 nF capacitors are hidden below the IC sockets.
1C51 control module
This module contains registers and some circuitry
for making the CPU able to set some control signals...
including baud rate selection.
2F51 flag and status module
Flags and status.
2R51 receiver module
That's the part which horribly failed,
and which isn't in the project files.
Unfortunately, this module is used in the X50 and X51 project.
2T51 transmitter module
Parallel to serial converter...
This module is used in the X50 and X51 project.
(c) Dieter Mueller 2015