Pentagon 128/512

The Pentagon 128 is also a Russian design but unlike the Scorpion it's not a brand name but a hardware design made in 1989. This means that a Pentagon can look and be very different. The one here is my Pentagon but I have also seen pictures of Pentagons in desktop cases. The Pentagon uses TR-DOS which makes it possible to use up to four disk drives. Standard RAM size is 512K but it's possible to have up to 4MB.

Some has TurboMode (7MHz, Z80B or Z80H), modem, CMOS-clock, kempston mouse, 2x AY, SoundDrive or Covox (first soundcards in russia), TurboMode for B-Disk Interface, 2HD format and so on... A 8 or 16K cache is also available to speed-up the disc operations. The new Beta-128 controller also use the HD disks with 1,7M capacity.

The current standard configuration is a Pentagon 512 Turbo, with 2 FDD (5.25" or 3,5") and Kempston mouse is standard. The most advanced version comes with a 7 MHz CPU (Z80B or Z80H) and 512K RAM. Two disc drives and a mouse comes as standard with this model.

Pictures

As the Pentagon is a hardware design the actual computers can look very different depending on who makes them. This is how my Pentagon looks anyway.

Pentagon 128 - front view
Front view. You can see the ventilation slots and the home made keyboard.

Pentagon 128 - side view
Side view with the printer port.

Pentagon 128 - back side
A rear view with the connectors and switches. From left to right: disk drive, reset, NMI(?), inverse video on/off, kempston joystick, RGB-connector, sound output, tape in/out, power.

Here is a more common design if the Pentagon in a desktop case and separate keyboard.

Connectors

TV

This connector is quite common on SECAM TVs which are used in France and Russia. The connector is a version of SCART and is known as Peritel or EuroConnector.

1	RED
2	GREEN
3	BLUE
4	comp.sync
5	sound
shield	ground

AY (sound)

The sound comes in ABC stereo, meaning that A is to the left, C to the right and B to both left and right.

1	n/c
2	ground
3	channel 2
4	n/c
5	channel 1

Kempston Joystick

A kempston joystick connector. Pin-out unknown so I could use some help here. I don't know about the Pentagon but this is the tape layout of the Robik.

1	left
2	down
3	up
4	fire
5	right
shield	ground

Tape

I don't know about the Pentagon but this is the tape layout of the Robik.

1	in
2	out
3	ground
4	?
5	?

Power

1	16 V
2	16 V
3	16 V
shield	ground

The Pentagon came in a few different versions. Versions 0,1 and 2 differs only by board layout and by number of used ICs (100 in version 0, 93 in version 1 and 89 in version 2). Two first versions has no AY sound chip layouted on the board and you have to use special "sound-chip board" with Z80CPU on it which have to be set into the place of Z80. Also version 2 does not have tape-in port anymore (nobody will use it if he has built-in disk drive controller). Version 2+ has very different timing, because it was made by other people than authors of initial 0, 1st and 2nd versions.