Click here for a list of the parts required to build an SC140, v1.0, Z180 SBC / Z50Bus Card.
WARNING: The oscillator is a very tight fit. It is essential that you fit the oscillator before fitting the 68-pin PLCC socket. See details below. Other than that, experienced builders can just go ahead and populate the board. There shouldn’t be any other 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 SC140, Z180 SBC / Z50Bus card should look like.
Resistors 2k2
Fit and solder the 2k2 resistors, R1 to R6 (shown below in red).
These can be fitted either way around, as they are not polarity dependent.
Resistors 100k
Fit and solder the 100k resistors, R7 to R9.
Resistor 1k
Fit and solder the 1k resistor, R11.
Resistor 10k
Fit and solder the 10k resistor R12.
Header sockets
Fit and solder the 6-pin angled header sockets, P2, P6, and P10.
Ensure they are fitted tight to the board.
Header pins (2-pin angled)
These may need to be cut from longer strips using wire cutters to cut the plastic.
Fit and solder the 2-pin angled headers, P4 and P8.
Header pins (6-pin angled)
These may need to be cut from longer strips using wire cutters to cut the plastic.
Fit and solder the 6-pin angled headers, P1, 56, and P9.
Ensure they are fitted tight to the board and the pins are parallel to the surface of the 6-pin angled sockets.
IC sockets
Fit and solder the 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.
Bus header
Fit and solder the Z50Bus header pins, P11.
Ensure the pins are parallel to the PCB so the card stands vertical when plugged in to a backplane.
Resistor network
Fit and solder the 8x10k resistor network, RP1.
The 10k network will be marked 103.
Take care to fit the resistor network the correct way around. Pin 1 is usually marked with a dot. This end is indicated on the PCB and on the illustration below.
Oscillator 18.432 MHz
Fit and solder the 18.432 MHz oscillator, X1. 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.
The oscillator is a tight fit between the sockets U4 and U6. Be sure to fit the oscillator tight up against the socket U6 as the slightest gap will make the fit against socket U4 even tighter.
PLCC socket
Fit and solder the 68-pin PLCC socket for U4.
This type of socket can be difficult to insert into the PCB holes as there are so many fragile pins, which must be carefully aligned.
The spacing around the oscillator is very tight and the socket U4 will slightly overlap the edge of the oscillator.
It is vital this socket is fitted the correct way around. The socket has a small chamfer on one corner, as indicated below in green
Quick Test
It is now worth repeating the check made earlier for a short on the power supply tracks. Connect the meter probes to each terminal of one of the capacitors, such as C1. This should be an open circuit, not a short.
Capacitor 1 nF
Fit and solder capacitor, C8.
This capacitor can be fitted either way around, as it is not polarity dependent.
The exact value of this component is not critical. The datasheet for the DS1233 specifies a value from 0.5 to 10 nF, thus a very low cost component with a wide tolerance is acceptable.
Capacitors 100 nF
Fit and solder capacitors C1 to C7.
These capacitors can be fitted either way around, as they are 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.
Header pins (straight)
These may need to be cut from longer strips using wire cutters to cut the plastic.
Fit and solder the pin header JP1 (1 row of 3 pins) (shown below in red).
Fit and solder the pin header JP2 plus PJ3 (1 row of 4 pins) (shown below in green).
Fit and solder the pin headers JP4, P3, and P7 (1 row of 2 pins), (shown below in blue).
Push button
Fit and solder the push button (reset switch), SW1.
Light Emitting Diode (LED)
Fit and solder green LED (LED1) in the position shown below.
The LED can either be fitted vertically, with straight leads, or horizontally, by bending the leads.
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).
Voltage supervisor and reset
Fit and solder the DS1233 voltage supervisor and reset device, U7.
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 where they enter the plastic casing. 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.
Quick Test (supply lines)
Repeat the check made earlier for a short on the power supply tracks. Connect the meter probes to IC U5 pin 20 (shown below in red) and U5 pin 10 (shown in green). 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 100 kΩ (100000 ohms) is acceptable.
Quick Test (reset line)
Now measure the resistance between IC U6 pin 1 (blue) and U6 pin 14 (red). This is measuring the pull up resistor, parts of RP1. It should read 5kΩ (5000 ohms) plus or minus 5%.
Also, measure the resistance between IC U6 pin 7 (green) and U6 pin 1 (blue). This is measuring the resistance of the reset switch (SW1). It should currently be open circuit. Again, the reading may take a few seconds to stabilise. A reading of more than 100 kΩ (100000 ohms) is acceptable. Whilst still measuring the resistance, press the reset button. The reading should now be a short circuit. A reading of less than 1 Ω is ideal, but less than 10 Ω is acceptable. The 10 ohm limit has been suggested mainly to allow for measurement accuracy with cheap meters.
Quick Tests (voltages)
Connect a 5 volt power source, typically using an FTDI style serial adapter to serial port A (P6) and fit a jumper shunt to P4.
- The voltage measured from U5 pin 20 (red) and U5 pin 10 (green) should be between 4.75 and 5.25 volts.
- Test the status LED by touching one end of a piece of wire to U6 pin 5 (medium blue) and the other end to U6 pin 7 (dark blue).
- The voltage measured from U6 pin 7 (dark blue) to U6 pin 1 (light blue) should be between 4.00 and 5.25 volts.
- The voltage measured from U6 pin 7 (dark blue) to U6 pin 1 (light blue) should be between 0.00 and 0.20 volts when the reset button is pressed.
- With a jumper shunt fitted to JP1 in the “write protect flash” position, check the voltage form U1 pin 31 (light orange) to U1 pin 16 (dark orange) is between 4.50 and 5.25 volts.
Integrated Circuits
If all the above tests check out okay, disconnect the power and insert the integrated circuits into their sockets.
Fit the Z180 CPU into its socket as illustrated to the right. This must be fitted the correct way around. The socket and IC both have a small chamfer in the position indicated.
Insert the other integrated circuits into their sockets, taking care to insert them the right way round, as illustrated below. Be careful not to bend any legs over.
Quick Test (reset)
Fit jumper shunts in the positions shown below.
Connect a 5 volt power source, typically using an FTDI style serial adapter to serial port A (P6) and fit a jumper shunt to P4.
An FTDI style serial adapter and cable is typically used to connect to the computer, as illustrated to the right.
The status LED should light for a fraction of a second, then blink off for about half a second, then light again. This indicates the self test has passed.
If the status LED does not perform as indicated above, try removing jumper shunt JP4 and briefly press the reset button. If the status LED now indicates the self test passed then the voltage supervisor U7 was probably holding the processor in reset. The usual reason for this is the supply voltage is not adequate. The voltage reaching the component on the PCB needs to be at least 4.75 volts.
Brief Test (serial port)
If the self test completes correctly, power down and connect serial port A to a computer running terminal software.
The terminal software should be set for 115200 baud, 8 data bits, no parity, 1 stop bit, and no flow control. Power up and you should see the startup message.
Given that the self test passed, a failure to display the start up message is most likely to be directly related to the serial port electronics or the serial adapter cable. Check for activity at the serial port connector and around the 2k2 resistors.
If all is well set the terminal software to use hardware flow control and check you still see the startup message. It is recommended that hardware flow control be used where possible.
Getting Started
The SC140 User Guide can be found here.
Other information about SC140 can be found here.
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