JonDent - Exploring Electronic Music: Tec 1D

Sunday, 24 February 2019

Tec 1D - computer

Some build notes for the Tec 1 computer.

This is a kit that came out in the early 1980s.

It's a single board computer with readouts in the form of a seven segment display.

It contains it's own PSU. It will also operate from a 6V battery. Battery back up is useful to avoid

loosing any programs written into RAM.

There is a 7805 regulator which keeps the operating voltage at 5V.

The PC layout of this board was done by none other than Ken Stone.

Notice the keyboard in the lower right of the photo. ... its really a keypad made up of switches. These are labelled with hexadecimal numbers 0 to F. There are also 4 switches.... labelled AD, GO, + and -.

AD = address
GO = excute the address (pushing it twice will run any program entered into the computer)
"+" = increment the address
"- " = decrement the address

This single-board kit computer was first produced by the Australian hobbyist electronics magazine Talking Electronics. It was featured in 1983, in Volume 1, Issue 10 of the Talking Electronics magazine, pages 57 to 75, with relevant chip data presented on the rear cover.

An early Tec-1 built by Ken Stone

Issue 11 featured add ons for the tec 1 --- ( two peripherals designed by Ken Stone for the TEC-1 -an 8x8 matrix display, and a relay driver board, allowing the TEC-1 to be interfaced to other equipment).

Volume 1, Issue 12, pages 13 to 38, had the third installment, including an interface for a simple plotter and a RAM expansion. TEC-1A was introduced in this issue with the PCB artwork presented on the inside rear cover.

Volume 1, Issue 13, pages 9 to 26, had the fourth installment,including a power supply designed specifically for it, and a non-volatile RAM module to allow data to be retained, even after the TEC-1 was powered off. (Wikipedia)

I'm building this as its a great way to understand basic computer architecture and learn the facts and operations of programming from ground level.

This is a TEC-1D Reproduction by Ben Grimmett (2018) It is based upon the PCB artwork of the TEC-1D

The unpopulated board.

The board came with a specially programmed chip ... called an EPROM (electrically programmable memory). The original board used a 16k bit 2716 EPROM.The new board requires a 32k bit 2732.
It is organized as 4,096 words by 8 bits.
This is directly above the speaker which can be used to play music.

The EPROM is NMOS Type with a UV Erasable Window.

That is it is housed in a 24 pin Window CeramicFrit-Seal Dual-in-Line package. The transparent lid allows the user to expose the chip to ultraviolet light to erase the bit pattern. A new pattern can be then be written to the device.

The computer contains 2K of RAM... programmed in machine code.
Machine code is very memory efficient and has a fast execution rate.... making high speed programs possible.

ic headers first.

A bit about the chips used in the original computer:
+ 8212 - Display Driver 1 --- drives each digit of the display
+ 8212 - Display Driver 2 --- drives segments A to G of the display
(The 8212s have been replaced with 74LS273s.
These are D-type flip flops....... also known as a latch ICs)

+ 2716 - EPROM
(the new board uses a 2732 EPROM)

+ 6116 - RAM
+ Z80 - CPU
+ 4049 - CMOS - the oscillator for the clock.
+ 74LS138 - (Logic gate address decoder) selects between EPROM (2716) & RAM (6116)
+ 74LS138 - (logic gate) selects between keyboard and display

Simplified block diagram.

The ROM contains all the information to start the computer and keep it running

The Z80 CPU is the arms and legs to which all instructions are sent. It does what the ROM requests.

The Z80 selects which device it wants to address by one of the two decoder 74LS38s
Because each decoder has only 4 outputs, we need two of them.

(Each 74LS38 logic chip has 4 gates with 2 inputs and one output).
Each selects one of 8 output lines.... going to the Keyboard or display & the ROM and RAM.

The 8212 Latch ICs (or 74LS273) drive the two LCD displays.
Because each has only 8 outputs we need two. The displays are multiplexed. The Z80 constantly feeds info into the displays via these 8212s.

The 74c923 chip feeds into the keyboard. The keyboard is constantly scanned by this chip. It scans the keys looking to see if any have been pressed.
If a button is pressed the 74c923 sends a 5-bit binary number (corresponding to the key).
Eg if key 5 is pressed it sends the number 00101.

The 2716 ROM tells the Z80 what to do when that binary number is received.

The 6116 is SRAM .... static RAM.

DIP-24 CMOS STATIC RAM 16K (2K x 8 BIT) IC

(There are 2 types of RAM ... Static & Dynamic)