Serial Terminal

A project log for Novasaur CP/M TTL Retrocomputer

Retrocomputer built from TTL logic running CP/M with no CPU or ALU

Alastair HewittAlastair Hewitt 11/25/2020 at 00:040 Comments

The first step in the serial terminal development was to echo characters typed on the keyboard to the screen. The new receive code is now integrated and echos text received over the RS232 serial interface to the screen as well.

The animated GIF below shows text being received over the serial connection at 9,600 baud, or 960 bytes per second. The text is 2.4k bytes and takes about 2.5 seconds to transfer (shown in real time).

The connection is made via a USB-to-RS232 null-model cable containing an FTDI chip. The cable includes a transmit and receive LED that can be seen below as both lit. This full duplex communication is possible by using two threads to handle both transmit and receive concurrently.

Each byte typed on the keyboard or received over the serial link is echoed back over the serial connection. The terminal program shown below is displaying the same text being transmitted after it is echoed back.

This was not a serious attempt to build a functional terminal program, but just a convienient way of testing the keyboard and serial interfaces. Next up is the virtual CPU testing, which should be a lot easier with a keyboard and a way to transfer code to/from the machine.