Click here for a list of the parts required to build an SC118, v1.1, Z80 Processor Card.
Experienced builders
There is only one suggested build option to watch out for. You can fit either a straight or a right angled header to P2 (serial port). Other than that there shouldn’t be any surprises to catch you out, so experienced builders can just go ahead and populate the board.
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 SC118, Z80 Processor Card should look like.
Resistors
Fit and solder the 470R resistor R1 (shown below in red).
Fit and solder the 10k resistor R2 (shown below in yellow).
These can be fitted either way around, as they are not polarity dependent.
IC sockets
Fit and solder IC sockets for U1 to U5 (shown below in yellow).
You may wish to fit a socket for oscillator X1 (shown below in red). My preference is to solder this component.
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.
Capacitors
Fit and solder capacitors C1 to C7 (shown below in yellow).
Fit and solder capacitor C8 (shown below in red).
These can be fitted either way around, as they are not polarity dependent.
Switch and LED
Fit and solder the push button switch SW1 (shown below in red).
Fit and solder the LED (shown below in yellow).
It is important to fit the LED the correct way around. LEDs usually have a small flat side to indicate the cathode (the negative end). This should be positioned to match the flat side shown on the circuit board (illustrated to the right). Also, the cathode pin on the LED is usually shorter than the other pin (the Anode).
The LED can either be fitted vertically, pointing away from the board, or the legs can be bent 90 degrees, so the LED lays flat against the board. Laying flat makes it easier to see when this card is mounted on a backplane with other cards.
Bus Connector
This connector is not needed if you only intend to use the board as a Single Board Computer (SBC) and never intend to fit it into a backplane.
Fit and solder bus connector P1.
You may need to cut the connector strip to length (if starting with a strip more than 25 pins long). Long nose wire cutters snip through the plastic quite easily.
Take care to ensure the pins are parallel to the circuit board so that the board will be vertical when plugged into a backplane.
Serial Header
Fit and solder connector P2.
You can either fit straight pins or angled pins.
Angled pins generally gives better access when mounted on a backplane, but fit straight pins if the card is to be used with card guides as suggested in the Z50Bus specification.
This header may need to be cut down from a longer strip.
Take care to ensure the pins are perpendicular (straight pin) or parallel (angled pins) to the circuit board.
Ground Test Point
Fit and solder header pins P3.
Oscillator
If you decided to solder the 7.3727 MHz oscillator, be sure to fit it the correct way around.
Pin 1 of the oscillator is normally indicated by a ‘sharp’ corner, while the other three corners are rounded.
Pin 1 on the circuit board is also indicated by a ‘sharp’ corner, while the other three corners are rounded.
Resistor Network
Fit and solder the 8x10k resistor network RP1.
This must be fitted the correct way around. The component should have pin 1 marked with a dot, as illustrated right.
Voltage Supervisor and Reset
Fit and solder the DS1233 voltage supervisor and reset device U6.
This device must be fitted the correct way around. Match the shape of the device to the legend on the circuit board.
It is necessary to spread the legs of the device to match the hole spacing on the circuit board. Do this gently so as too avoid straining the legs. DO not press the component hard into the board as this will also strain the legs.
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.
With a suitable FTDI style TTL level serial to USB adapter connected from P2 to a powered USB socket, check the supply voltage on this circuit board between U4 pin 7 and U4 pin 14. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts. Unplug the serial adapter.
Integrated Circuit U5
Insert the IC U5 (74HCT259) into its socket, taking care to insert it the right way around, as illustrated below. Be careful not to bend any legs over.
Test
With a suitable FTDI style TTL level serial to USB adapter connected from P2 to a powered USB socket, check the LED lights. If not then follow these steps.
- Check the supply voltage between U5 pin 8 and U5 pin 16. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts.
- Check the LED is the correct way around.
- Check the RESET signal is high but goes low when the reset button is pressed. The LED should light when U5 is powered and working, and the RESET signal on U5 pin 15 is low. With the other ICs not fitted the LED may not stay on after the RESET signal goes high.
Do not continue assembly until the LED is working.
Integrated Circuits
Insert the ICs into their sockets, taking care to insert them the right way around, as illustrated below. Be careful not to bend any legs over.
Oscillator
If you elected to fit a socket for oscillator X1, then insert the oscillator now. See instruction above regarding orientation.
Quick Start Guide
Below is a very brief guide to getting started with the SC118, Z80 Processor Card. For further details so the SC118 User Guide.
The ROM should contain the Small Computer Monitor v1.0 configuration F1.
Connect a suitable FTDI style TTL level serial to USB adapter from P2 to a powered USB socket on a PC (or similar). These adapters come in many different shapes and sizes. The picture below shows one possible configuration.
Press the reset button and check the LED lights. It should flash off and on again, twice, and then remain on.
Start a suitable terminal emulation program, such as Tera Term, on the PC (or equivalent). Configure the PC’s serial port for 9600 baud, 8 data bits, 1 stop bit, no parity and hardware flow control (RTS/CTS). There is no need to set the terminal software to add delays. Almost any terminal emulation should work with the Small Computer Monitor.
Press the reset button on the SC118 Processsor Card. You should see the terminal program display something like “Small Computer Monitor – F1”.
You are now ready to play!
Fault Finding
Check there are no chips with bent legs and thus not making contact with their socket, carefully inspect all soldering, check all the chips are inserted the right way around, check all the components are in the right place.
With a suitable FTDI style TTL level serial to USB adapter connected from P2 to a powered USB socket, check the supply voltage on this circuit board between, say, U4 pin 7 and U4 pin 14. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts. Insufficient voltage can lead to the DS1233 Voltage Supervisor holding the reset line low.
Check the LED is on. If it is not, then check the LED is the correct way around. Also check the RESET signal is high but goes low when the reset button is pressed. The LED should light when U5 is powered and working, and the RESET signal on U5 pin 15 is low.
If the LED is working, check it flashes off then on again, either once or twice after a reset. If it flashes then the motherboard is running code successfully. This would indicate that all the main components are generally working. If the LED flashes off once after reset the system has detected a serial card plugged into one of the Z50Bus. If it flashes off twice it has not detected a serial card and is using the onboard serial port (P2). If it keeps flashing the self-test has failed, most likely indicating the RAM is not working.
Small Computer Central 