SC511 is a serial interface and timer card for the Z50Bus.
Documentation
- SC500 – Series Information
- SC511 – Description
- SC511 – Assembly Guide
- SC511 – Parts List
- SC511 – Printed Circuit Board
- SC511 – Support
- SC511 – User Guide
Downloads
Kits
Examples
Description
The SC511, serial and timer card houses a Z80 SIO chip, which provides two TTL serial ports for use with FTDI style serial adapter cables, and a Z80 CTC, which has four counter/timer channels.
The main features of this card are:
- Z50Bus compatible (“Standard” card size 100mm x 75mm)
- Full Z80 mode 2 interrupt support (IEI/IEO daisy-chain)
- Interrupt look-ahead circuit
- Two TTL serial ports for use with FTDI serial adapter cables
- Software control of baud rate for both ports
- On-board oscillator for independence from CPU clock rate
- Clock tick timer
- Two I/O address options
- Optional connection of either port to Z50Bus RX/TX pins
Parts List
| Reference | Qty | Component |
| PCB | 1 | SC511, v1.0, PCB |
| C1 to C6 | 6 | Capacitor, ceramic, 100 nF |
| JP1 and JP2 | 2 | Header, male, 1 x 2 pin, angled |
| JP3 and JP4 | 2 | Header, male, 1 x 3 pin, straight |
| JP5 plus JP6 | 1 | Header, male, 1 x 6 pin, straight |
| Jumper shunts | 8 | Jumper shunt Two used to pad box header |
| P1 | 1 | Box header, 2 x 25 pin, angled, or Header, male, 2 row x 25 pin, angled |
| P2 and P3 | 2 | Header, male, 1 x 6 pin, angled |
| R1 to R8 | 8 | Resistor, 2k2, 0.25W |
| R9 to R12 | 4 | Resistor, 100k, 0.25W |
| R13 | 1 | Resistor, 10k, 0.25W |
| S1 and S2 | 2 | Header, female, 1 row x 6 pin, angled |
| Spacer | 1 | Spacer, 10mm, M3, nylon |
| Screw (for spacer) | 1 | Machine screw, 6mm, M3 |
| U1 | 1 | 74HCT138 |
| U1 socket | 1 | 16-pin DIP socket |
| U2 | 1 | Z80 SIO/2, Z84C4208PEG, or Z80 SIO/2, Z84C4210PEG |
| U2 socket | 1 | 40-pin DIP socket |
| U3 | 1 | 74HCT08 |
| U3 socket | 1 | 14-pin DIP socket |
| U4 | 1 | Z80 CTC, Z84C3008PEG, or Z80 CTC, Z84C3010PEG |
| U4 socket | 1 | 28-pin DIP socket |
| X1 | 1 | Oscillator, 1.8432 MHz Solder to PCB recommended |
| X1 socket | 1 | 8-pin DIP socket Socket not recommended |
Printed Circuit Board
| Supplier | Website | Ships from |
| Stephen C Cousins | Tindie | UK |
| pcb4diy | pcb4diy.de | Germany |
| pcb4diy | eBay | Germany |
User Guide
The SC511, serial and timer card houses a Z80 SIO chip, which provides two TTL serial ports for use with FTDI style serial adapter cables, and a Z80 CTC, which has four counter/timer channels.
Powering the system
Fitting jumper shunts to headers JP1 and/or JP2 connect the FTDI style 5-volt serial port’s power pin to the card’s 5 volt supply. This enables the retro computer system to be powered from the serial port, or a device connected to the serial port to be powered from this card.
Alternatively, power can be supplied from the Z50Bus.
Do not attempt to power the system from two different sources. If the system is not being powered from a serial port, then only fit a jumper shunt to JP1 or JP2 if the serial device is being powered from the system.
Serial on the Z50Bus
The Z50Bus has two lines dedicated to a serial interface. This enabled two cards to communicate via the bus rather than having to have additional cables between the cards.
Jumpers JP3 and JP4 enable one of the serial ports to be connected to the Z50Bus RX and TX lines. Each jumper has two positions: A and B. Position A links the port A signals to the bus, while position B is for the port B signals. Leave the jumper shunts off to isolate this card’s RXD and TXD signals from the Z50Bus.
Address Selection
Jumpers JP5 and JP6 allow the address ranges of the SIO and CTC chips to each be set to one of two options. Each chip occupies four I/O addresses. The addresses should be set to either:
| Card | SIO | CTC |
| Primary | 0x80 to 0x83 | 0x88 to 0x8B |
| Secondary | 0x84 to 0x87 | 0x8C to 0x8F |
The primary addresses are the defaults supported by the current firmware. A second card can be added to the system with the secondary addresses selected, but there is not currently any software to support this.
The illustration below shows the default positions for the jumper shunts on JP3 to JP6.
Serial Ports
Two FTDI style 5-volt serial ports are provided at P2 and P3.
The pin-out, below, describes signals with respect to the card, so an output is a signal from the card to a computer or terminal.
| Pin | Function |
| 6 | Clear To Send (CTS) input to the card |
| 5 | Transmit Data (TxD) output from the card |
| 4 | Receive Data (RxD) input to the card |
| 3 | Vcc (5V) |
| 2 | Request To Send (RTS) output from the card |
| 1 | Ground (GND) |
The serial ports settings depend on the firmware or software being run. Typically these are:
| Setting | Port A | Port B |
| Baud rate | 115200 | 9600 |
| Data bits | 8 | 8 |
| Stop bits | 1 | 1 |
| Parity | None | None |
| Flow control | Hardware RTS/CTS | Hardware RTS/CTS |
Current firmware assumes the use of serial port A as the default console device.
Counter / Timer
The Z80 CTC is a four-channel counter/timer interface. The channels are used as follows:
- Channel 0: Serial port A baud rate clock
- Channel 1: Serial port B baud rate clock
- Channel 2 and 3: Clock tick generator/timer
The output of channel 2 is connected to the input of channel 3. This makes a flexible clock tick generator or timer.
For full details search for Z84C30 datasheet or the Zilog Z80 Family CPU Peripherals User Manual (UM0081).
Clock Source
This card has its own oscillator as a clock source for the CTC, making the serial port and timer functions independent of the CPU’s main clock.
Software and Firmware Support
Z80 systems with the Small Computer Monitor in ROM:
Plug this card and a Z80 processor card, such as SC118, into a suitable backplane. Connect an FTDI style serial to USB adapter from serial port A (S1 or P2) to a computer running a terminal emulation program. The terminal should be configured for 115200 baud, 8 data, 1 stop, no parity. Flow control can be either Off or hardware RTS/CTS.
Turn the power on. The terminal should show something similar to the illustration below.
Z180 systems with RomWBW:
This card is not supported in the 3.0.1 release version of RomWBW, but you can download the latest pre-release version from the development branch and configure it for this card. Later release versions of RomWBW should include support for this card.
Assembly Guide
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.
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 SC511 Serial and timer card should look like.
Resistors
Fit and solder the eight 2k2 resistors, R1 to R8 (shown below in yellow).
Fit and solder the four 100k resistors, R9 to R12 (shown below in red).
Fit and solder the 10k resistor, R13 (shown below in blue).
These can be fitted either way around as they are not polarity dependent.
Sockets (6-pin)
Fit and solder the 6-pin angled sockets, S1 and S2.
Ensure the socket lays flat against the circuit board.
IC sockets
Fit and solder the IC sockets for U1 to U4 (shown below in red).
You may wish to fit a socket for oscillator X1 (shown below in blue). My preference is to solder this component as I like low-profile boards.
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.
Serial header
Fit and solder the serial port header pins, P2, P3, JP1, and JP2.
You can either fit these as a single continuous strip, by pulling out the unwanted pins with pliers, or you can cut the strip into the correct side for each header.
Capacitor 100 nF (0.1 µF)
Fit and solder capacitors, C1 to C6.
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.
Jumper pins
Fit and solder jumper header pins, JP3 and JP 4 (shown below in blue).
Fit and solder jumper header pins, JP5 and JP6 (shown below in red).
These can be fitted as a single strip of 6 pins.
Oscillator
If you decided to solder the 1.8432 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.
Bus connector
Fit and solder the bus connector, P1. This can either be a right-angled box header or right-angled header pins. The box header is recommended.
Take care to ensure the 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.
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 S1 or P2 to a powered USB socket, and a jumper shunt fitted to JP1, check the supply voltage on this circuit board between U3 pin 7 and U3 pin 14. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts. Unplug the serial adapter.
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.
If you fitted a socket for the oscillator, X1, fit the oscillator now.
Test
Fit a jumper shunt to JP5 and another to JP6, in the positions shown below in red. These select the default address for the SIO and CTC chips.
If the system is to be powered from one of the serial ports, fit a jumper shunt in one of the positions indicated below in yellow. The default port is normally port A, so JP1 is the most likely position to fit a jumper shunt.
Do not attempt to power the system from two different sources. If the system is not being powered from a serial port, then only fit a jumper shunt to JP1 or JP2 if the serial device is being powered from the system.
The jumpers shown in blue are optional. They are only needed if you wish to connect one of the serial ports to the Z50Bus RX and TX lines. To connect serial port A to the bus lines, fit the shunts in the positions shown below in blue.
You are now ready to play!
Z80 systems with the Small Computer Monitor in ROM:
Plug this card and a Z80 processor card, such as SC118, into a suitable backplane. Connect an FTDI style serial to USB adapter from serial port A (S1 or P2) to a computer running a terminal emulation program. The terminal should be configured for 115200 baud, 8 data, 1 stop, no parity. Flow control can be either Off or hardware RTS/CTS.
Turn the power on to the system. The terminal should show something similar to the illustration below. Check the SC511 user guide for more information.
Z180 systems with RomWBW:
This card is not supported in the 3.0.1 release version of RomWBW, but you can download the latest pre-release version from the development branch and configure it for this card. Later release versions of RomWBW should include support for this card. Check the SC511 user guide for more information.
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 S1 or P2 to a powered USB socket, check the supply voltage on this circuit board between, say, U3 pin 7 and U4 pin 14. This should be 4.5 to 5.5 volts, preferably 4.75 to 5.25 volts.
If your system is running the Small Computer Monitor and you have a means of displaying the self-test results, typically an LED output, check if the serial port has been detected. See the processor card and SCM documentation for details.
If the serial port has not been detected, the problem is probably one of the signals from the Z50Bus to the SIO.
If the serial port has been detected, the main bus connections and SIO chip are probably good. Remove the card from the backplane. Connect a powered FTDI style cable to port B header (S2 or P3) and fit jumper shunts to JP1 and JP2. Now check these voltages on port A header (S1 or P2):
- Pin 1, GND, less than 0.1 volts
- Pin 2, /RTS, more than 4.5 volts
- Pin 3, 5V, more than 4.5 volts
- Pin 4, RXD, more than 4.5 volts
- Pin 5, TXD, more than 4.5 volts
- Pin 6, /CTS, less than 0.4 volts
If you have a logic probe or oscilloscope, check the output of the oscillator (X1). This should be 1.8432 MHz.
Notes
- This design is made with the permission of LiNC (designers of the Z50Bus).
- This product is designed for hobby use and is not suitable for industrial, commercial, or safety-critical applications.
- The product contains small parts and is not suitable for young children.
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