April/May 1980, Issue 7

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The ribbon cartridge is about 2″ wide, by the full 10″ width of the platten. The ribbon is in the form of a continuous loop, and is driven by a small capstan and pinch roller inside the cartridge. Drive to the ribbon is by a small tongue which engages in a slot in the ribbon capstan, and is driven from the head drive spiral. The ribbon cartridge appears to hold an enormous amount of ribbon, probably about 50 yards which should last a few million characters. Don’t open one and spill the contents on the floor, it takes hours to wind it back. The ribbon cartridge is slightly ‘skewed’ in its mounting so that the left hand side is lower than the right, this is so the head traverses the ribbon diagonally, therebye avoiding ribbon wastage.

The Electronics

The electronics are quite a surprise, as they are loosely based on a Nascom, using a Z80 processor, 1K RAM, 2K ROM, PIO and UART (add a video RAM and a keyboard port and you could very well have a Nascom 1). A proper crystal controlled baud rate generator is fitted, and this also provides the system clock. Power transistors driven by the PIO feed the needle solenoids and stepper motors. The whole of the circuitry is mounted an the double sided pcb of the usual Nascom standard, with the main smoothing capacitor mounted on a bracket over the pcb

All the printer timing functions are software derived and controlled by the CPU which is being used in an interrupt driven mode. Incoming data is stored in the RAM, which has about 950 bytes free as buffer storage. The buffer is organized as a ‘first in first out’ file and a handshake signal goes active low when the buffer has only ten bytes free. Parity’ and ‘carriage return, carriage return/​line feed’ options are link selectable, as are the input BAUD rates between 75 and 9600 BAUD. Interestingly, the baud rate generator also outputs a clock signal at 16 times the selected baud rate so that the Imp can drive the sending device UART at speeds higher than normally be possible.

Internally the Imp’s appearance is functional but untidy. The mechanism chassis and the pcb both being mounted on a heave gauge black anodized aluminium pressing. The connecting cables to mains transformer and function switches are secured by ‘double side-sticky’ to the tops of components on the pcb. Not exactly professional practice, but adequate.

The Imp is cased in an attractive (although slightly too ‘bright’) blue moulded plastic cover, which whilst flexible appeared robust enough for the purpose. It is unfortunate that Nascom have succeeded in making this very cheap and functional printer look cheap as well. The metallized stick-on plastic strip right across the front, bearing the legend ‘Nascom micro IMP’ in letters 1.5″ high completely ruins the otherwise neat appearance. A small discreet badge would have been a much better idea.

On Test

On unpacking the IMP, it was immediately apparent that the packing would not adequate in the hands of the Great British Post Office, and we suggest that the paper roll carrying arms be removed

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