Elektor_Mag_-_January-February_2021

42 January & February 2021 http://www.elektormagazine.com

erable number of peripherals: a 64 kB EEPROM for ‘mass storage’,

while 8 digital inputs and 24 digital outputs provide communication

with the outside world. These 32 I/Os allow the usual interfaces

(RS232, I^2 C and SPI) to be realised in software.

“This single-board computer can achieve a surprising number of

things. For example, I built a simple calculator in the operating

system that can be operated via the RS-232 interface. This calcu-

lator primarily serves as proof that floating-point operations can

be carried out by a single NOR-gate! Furthermore, the operating

system contains a simple monitor program that allows assem-

bly-language instructions to be entered. This way you can write

your own assembly-language programs directly on MyNOR and

store them in the EEPROM (this is a bit in the style of the C64).

But it is, of course, also possible to upload a complete program.

This is done using a text file that represents the binary program

in a special format. A little bit of patience is required because the

connection at 2400 baud is not blindingly fast.

“It becomes really exciting when this single-board computer is

used without the umbilical cord to a PC. For this purpose I have

developed two expansion boards. The first contains 20 pushbut-

tons, an LED and eight 7-segment displays along with the requisite

transistors for driving them. The displays and pushbuttons are

multiplexed in the usual way. I use the ‘pocket calculator’ built in

this manner every day at work.

“The second expansion board turns MyNOR into a real small

computer. This board contains, in addition to the usual pushbut-

tons, a 4 × 20 LCD, a little loudspeaker, a battery-backed real-time

clock and a temperature sensor. When MyNOR is expanded with

this board there are an endless number of possibilities: I have

already programmed a few games (minesweeper, Tetris), a kitchen

tives have become too complicated. And, secondly, it would have

to suffice with a single programmable memory IC (EEPROM).

“My new computer uses only a single NOR-gate for its arithmetic

• an extremely simple logic unit that I chose because it is easily
  built using two MOSFET transistors and a resistor (Figure 2). All
  arithmetical operations (such as AND, OR, EXOR, add and subtract)
  are obtained in software from combining many individual NOR
  operations.

“Because of the central NOR gate I have christened my new

computer MyNOR [2]. The total number of parts is so few that the

entire circuit fits on a circuit board measuring 10 × 13 cm. Figure 3

shows the formal portrait of MyNOR, while the photo on the right

shows what is where on the circuit board. It also contains a consid-

Figure 4: The pocket calculator on the left and, on the right, the MyNOR

with keyboard and display.

Figure 3: The final version of MyNOR. The description on the right shows that a considerable amount of functionality is possible.