The Nascom 3 was basically a Nascom 2 computer kit, but sold as a pre-assembled kit, with a nice molded case.
The Nascom 1 and 2
The Nascom 1 and 2 where single-board computer kits produced between 1977 and 1979 in the United Kingdom. They were based of the Zilog Z80 CPU and came with a keyboard, a video interface, a serial port, and two 8-bit parallel ports. The serial port could be used to store data on tape using the Kansas City encoding standard.
The computers were kits, which meant that the buyer had to assemble them. As such it was unique that they came with a full keyboard and video interface. Assembling the unit consisted of soldering over 3000 joints on the circuit board.
The system was designed around the Z80 CPU and the Z80 PIO (Programmable I/O) chip. It also had a 6402 UART for serial communication and memory mapped video display that used a character generator. The Nascom 1 and 2 used 16 rows of 48 characters. Each row of characters used 64 memory locations. The extra 16 locations were hidden by video blanking. The characters were generated by the MCM6576P Character generator, which could generate 128 characters. The Nascom 2 also had a second character generator ROM that was used to display graphics characters. The machine came with Microsfot Basic built into an 8K ROM that used the graphics characters to create a blocky 96x48 semi graphics mode.
The CPU and video circuit shared the same RAM, but the CPU had RAM priority. If the CPU would write to RAM while the video circuit was reading from it, it could cause flickering on the display.