SBC V2-004

The SBC V2 is a Zilog Z80 processor board. It's a 100x160mm board that is capable of functioning both as a standalone SBC or as attached to the ECB bus.

Previously known as the N8VEM SBC, development began in 2006 wth V1 and is currently still in development.


  • 4Mhz+ Zilog Z80 CPU.
  • Up to 512Kb paged SRAM.
  • Up to 1Mb EPROM or 512Kb Flash ROM.
  • Serial Interface.
  • IDE interface.
  • Real Time Clock.
  • Onboard sound.
  • Battery backup for RTC and SRAM via super capacitor.
  • Standard ECB bus interface.
  • +5V power connector for Single Board Computer operation.
  • Reset button.
  • Status LED.
  • Switchable clock speed.


Changes from SBC V2-003A

  • Addition of speaker circuit.
  • Add solder jumpers for bypassing DS1210.
  • Move status LED to corner of board as per other ECB boards.
  • Align serial connector pinout and functionality to SBC Z180 Mark IV
  • Add max232 solder jumpers for TTL level output.
  • Add onboard super capacitor.
  • Incorporate ppide.
  • Update to Kicad 5.
  • Add jumper settings to silkscreen.
  • Move reset switch to edge of board and remove reset jumper.
  • Add jumpers to configure battery backup source.
  • Add cpu clock divider to support MSX.
  • Default to hard Kontron reset mode.
  • Add User input button on UART Ring Indicator line (for recovery mode in ROMWBW)
  • Elimination of flow control jumpers.

Software Support

ROMWBW BIOS featuring:

  • CP/M / ZSDOS
  • RAM & ROM disk support.
  • ROM based BASIC, FORTH and Monitor.
  • Prebuild disk images

ROMWBW Eurocard expansion board driver support:

  • VDU
  • CVDU
  • VGA3
  • Zilog Peripherals
  • Disk I/O
  • 4PIO
  • SCG
  • DSKY
  • MF-PIC

Most recent Kicad files can be found here:

Parts List

Reference#Value DIP8DIP14DIP16DIP20DIP32DIP40
C1,C3-C23,C29,C30,C32,C33160.1uFCeramic Capacitor
C2110uFElectrolytic Capacitor
C31122uFElectrolytic Capacitor
C24-C2741uFElectrolytic or Tantalum Capacitor
C28 (REV V)110uFElectrolytic Capacitor
C3410.22FSuper Capacitor
D115mm LEDRed/Green Bicolor
K1,K6-K1391×3Pin Header 3 position 2.54mm
JP1, JP2, LS1,P641×2Pin Header 2 position 2.54mm
P112×2040 pin IDC vertical socket.
P212.1mmBarrel Jack Socket
P312×510 pin IDC vertical socket.
P414/8MhzCPU Clock 5V Active crystal oscillator square socket1
P511.8432MhzUART Clock 5V Active crystal oscillator square
Q112N3906PNP Transistor
SW116x6mmMini Push Button Switch DIP 4pin
R1110R0.25w resistor
R2,R11210K0.25w resistor
R91100R0.25w resistor
R1214K70.25w resistor
R1313K60.25w resistor
R1411K80.25w resistor
R151120R0.25w resistor
R161470R0.25w resistor
RR111KSIP-6 Resistor array
RR214K7SIP-6 Resistor array
U1116550UART DIP40 socket 1
U2127C080EPROM 512kb DIP32 socket 1
U3174LS08Quad 2-in AND Gate DIP14 socket 1
U4174LS10Triple 3-Input NAND Gate DIP14 socket 1
U5174LS125Tri State Quad Bus Buffer DIP14 socket 1
U6174LS139Dual 1-of-4 Decoder/De-multiplexer DIP16 socket 1
U7,U27274LS14Hex Inverter/Schmitt Trigger DIP14 socket 2
U10174LS243Quad Bus Transceiver DIP14 socket 1
U8,U9,U11374LS245Octal tri-state bus transceiver DIP20 socket 3
U12,U13,U18374LS174Hex D-type flip flop with clear DIP16 socket 3
U14-U16374LS32Quad 2-input OR gate DIP14 socket 3
U17174LS244Octal Driver Tri-State DIP20 socket 1
U1918255Programmable Peripheral Interface DIP40 socket 1
U201C96ABCDIN 41612 Connector, 96 pin plug, right angle.
U211DS1302Maxim Trickle-Charge Timekeeping Chip DIP8 socket1
U221MAX232Maxim Multichannel RS-232 Drivers/Receiver DIP16 socket 1
U231AS6C4008512Kb x 8 RAM or AS6C1008 128Kb x8 RAM DIP32 socket 1
U241Z84C00Z80 CPU DIP40 socket 1
U251DS1210Maxim Nonvolatile Controller Chip DIP8 socket1
U26174LS06Hex inverter buffers/drivers DIP14 socket 1
U28 (REV V)174LS74Dual D-Type Positive Edge Triggered Flip Flop DIP 14 socket 1
X1132.768KHz3mm Crystal 6pF
DIP Sockets 3115423


Default setting with Super capacitor, DS1302 RTC, DS1210 Power Manager, 27C080 EPROM and AS6C4008 512Kb RAM Installed:

JP1BATSELOPEN - CLOSEDOPENDisconnect RAM and RTC from ECB bus backup power.
JP21BIT-INOPEN - CLOSEDOPENDo not use ROMWBW console switch facility.
JP9RECOVERYOPEN / CLOSEDOPENPin header to recovery mode button (version Z)
K1A171-2 / 2-31-227C080 EPROM Installed.
K6A181-2 / 2-31-227C080 EPROM Installed.
K7128/5121-2 / 2-31-2AS6C4008 512Kb RAM Installed.
K8A191-2 / 2-31-227C080 EPROM Installed.
K9PWR1-2 / 2-31-2Disconnect 5V from IDE connector.
K10BNKSEL1-2 / 2-31-2Select top of RAM to be fixed, bottom to be switchable.
K1116K/32K1-2 / 2-31-2Select top fixed RAM size to be 32Kb.
K12INTSEL1-2 / 2-31-2Connect 16550 UART to interrupt line.
K13RSTSEL1-2 / 2-32-3Select KONTRON reset method. (Removed)

Jumper Descriptions

JP1BATSEL - Battery Select

Retention of memory and RTC time and data is supported on the SBC V2. The source of backup power to the memory and RTC is controlled by JP1. Power from the on-board super capacitor and/or from the ECB-BUS backup power line can be selected.

Closing JP1 will connect the ECB bus backup power in parallel with the onboard super capacitor. If JP1 is open then only the super capacitor will provide backup power. The DS1302 can be configured through software to provide charging power to the on board super capacitor and other power sources connect to the ECB bus backup power line. If the power source does not support charging i.e. battery then JP1 should be left open.

JP21BIT-IN - 1 Bit input

Do not use ROMWBW console switch facility.

JP3RAMVCC - RAM 5 Voltage
JP4RAMCS - RAM Chip Select

The DS1210 Power Manager provides controlled switchover to battery / supercapacitor on power down for the RAM and RTC to prevent corruption.

If the DS1210 is not installed then these solder jumpers should be bridged so that the CS and VCC power are connected to the RAM.

JP5RXD TTL solder bridge
JP6CTS TTL solder bridge
JP7TXD TTL solder bridge
JP8RTS TTL solder bridge

Link all solder bridges for TTL level RS232 signals when MAX232 is not installed.

K1 A17 - Address line 17
K6 A18 - Address line 18
K7 A19 - Address line 19

These three jumpers are used for configuring the type of EPROM or FLASH memory being used. See below for examples.

K7128/512 - 128Kb or 512Kb RAM option.

Selects the size the RAM chip installed by routing either VCC ( 5V) or address line 17 to pin 30 of RAM chip U23. ROMWBW defaults to 512Kb RAM. If 128Kb RAM is installed then a custom ROM image should be regenerated with the following option:



Jumper 1-2 if an AS6C4008 512Kb RAM is installed or jumper 2-3 if a AS6C1008 128Kb RAM is installed.

K9PWR - Power to IDE connector option
K10BNKSEL - Bank Selection option
K1116K/32K - 16K or 32K fixed RAM top option
K12INTSEL - Interrupt select option
K13RSTSEL - Reset select option.

The Retrobrew ECB bus is based on a design called the Kontron bus,. Early Retrobrew ECB bus and board designs incorrectly implemented the RESET circuit design. This jumper allows the SBC V2 to be configured for the corrected design call KONTRON or the older design (LEGACY / N8VEM). All board in a system must use the same reset style. Most newer boards have an option to select either style but older boards are hardwired for LEGACY / N8VEM style reset.

Jumper 1-2 for LEGACY / N8VEM style reset or 2-3 for KONTRON style. Option removed in final version. Now hardwired for KONTRON mode.




Version U - Silkscreen mixed up for R1 and R2 resulting in reset button failing. R2 should be resistor closest to reset jumper and should be 10K. R1 is resistor closest to reset switch and should be 10R. Lots of silkscreen reverted to Fab layer somehow. Fixed in revision R

Version V - CPU oscillator may not work due to incorrectly placed pull up resistor. A 1k resistor needs to be added between pin 12 and pin 14 of U26 74LS06.

boards/sbc/sbc_v2/sbc_v2-004.txt · Last modified: 2020/12/03 04:10 by b1ackmai1er
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