Click here for a list of the parts required to build an SC514, v1.0, Z80 CTC card.

Important note: How to modify box headers

Experienced builders can just go ahead and populate the board. There shouldn’t be any surprises to catch you out.

Introduction

This guide assumes you are familiar with assembling circuit boards, soldering, and cleaning. If not, it is recommended you read some of the guides on the internet before continuing.

First check you have all the required components, as listed in the parts list.

Before assembling it is worth visually inspecting the circuit board for anything that looks out of place, such as mechanical damage or apparent manufacturing defects.

If you have a multimeter that measures resistance or has a continuity test function, check there is not a short on the power supply tracks. Connect the probes to each terminal of one of the capacitors, such as C1. This should be an open circuit, not a short.

The picture below shows what a completed SC512 should look like.

Resistors

Resistors can be fitted either way around, as they are not polarity dependent.

IC sockets

Be sure to fit them with the notch matching the legend on the circuit board, so you do not end up fitting the IC the wrong way around too.

Soldering the oscillator directly to the PCB is recommended, but if you would rather use a socket then fit the socket now.

Resistor network

Double row angled header pins

Header JP1 is the 6 address select jumpers that are labelled with their bit numbers. The card occupies 4 addresses, thus address bits 0 and 1 are not included in the address decoding. The board includes placeholders for bits 0 and 1 for consistency with other cards in the SC500 series. It is suggested that you remove or cut the pins for bits 0 and 1 as a reminder that they are not used.

Double row straight header pins

These can be fitted as eight short lengths or two long lengths with pins removed for the gaps between sets. Pins can be pulled out with pliers.

Bus connector and I/O connector

Take care to ensure the bus connector is fitted such that the card will stand vertically when fitted to a backplane. A good method is to just solder two pins, one at each end, and then check it looks correct. Then solder two more, one at each end but in the other row, and check again. At each stage, if necessary, adjust the position by heating the required solder joint and moving the connector slightly. Solder two pins in the middle of the connector and check again. Then solder all the others.

Capacitor 100 nF (0.1 µF)

This capacitor can be fitted either way around, as it is not polarity dependent.

The exact value of this component is not critical. The use of very cheap capacitors within the range of about 30 to 200 nF is acceptable.

Capacitor (100uF)

The silkscreen has a plus sign for the positive terminal and a hashed area for the negative terminal.

Oscillator

Pin 1 on the circuit board is indicated by a square pad and a small ‘dot’. See illustration below.

The circuit board allows for the use of either a half-size (8-pin DIP style) or a full-size (14-pin DIP style) oscillator. In each case, the component only has 4-pins, one in each corner.

Inspection

Remove any solder ‘splats’ with a brush, such as an old toothbrush.

Visually inspect the soldering for dry joints and shorts.

Clean the flux off with suitable cleaning materials.

Visually inspect again. The importance of visual inspection can not be overstated.

Quick Test

Check for a short on the power supply tracks by measuring the resistance between IC U1 pin 20 and U1 pin 10 (indicated below). This should be an open circuit, not a short. If you are using a digital meter set to measure resistance it will likely take a few seconds for the reading to stabilise as there are now capacitors on the power lines. A reading of more than 100k Ω (100000 ohms) is acceptable.

Integrated circuit

Insert the integrated circuits (ICs) into their sockets, taking care to insert them the right way around, as illustrated below. Be careful not to bend any legs over.

Address select jumpers

The card responds to input/output addresses matching the address set with jumpers. When a jumper shunt is fitted, that bit must be a 1 (high voltage). When the shunt is not fitted, that bit must be a 0 (low voltage).

Header JP1 is the 6 address select jumpers that are labelled with their bit numbers. The card occupies 4 addresses, thus address bits 0 and 1 are not included in the address decoding. The board includes placeholders for bits 0 and 1 for consistency with other cards in the SC500 series. It is suggested that you remove or cut the pins for bits 0 and 1 as a reminder that they are not used.

The recommended base address is currently 60 hex (01100000 binary) when used as part of an SC500 system. This address is selected by fitting jumper shunts for bits 6 and 5. A CTC at this address is not used by any current system software, such as for the system timer or baud rate clock generator.

It is possible to use this card as a system timer by setting the base address to 0x88. Current system software assumes a CTC at this address uses channels 0 and 1 for baud rate clock generators and channels 2 and 3 for the system timer.

You are now ready to give it a try.

The SC514 User Guide is here.