1. Andrew Jessop Avatar Andrew Jessop
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PCB Design

LPC Module Pin assignments

  • More detail in: SCSI Pinout
  • 30 pins for SCSI (see table at SCSI-Spec/SCSI2-05.html#5.6.3 )
  • 5 pins for SD Card (DI,DO,SCLK,CS,EN)
  • 2 pins for UART (P0.2, P0.3) USB Uart Module, FT232RL
  • 1 pins for bootloader enable switch (P2.10)
  • x pins for status LED(s)
  • 2 pins for USB interface (P0.29, P0.30)

TODO

  • ACK, REQ, SEL, BSY, RST Resistors
  • Molex voltage & current measurement via ADC/opamp and current shunt resistor. (Need to choose a suitable current measurement chip).

Complete

  • Reset Circuit.
    • Reset has an external pull-up on the LPC1768 module with a push button.
    • Connect USB Uart Module CTS pin to RST to enable manual or automatic programming.
    • Connect USB Uart Module DTR pin to P2.10 (Bootloader Enable pin) to enable manual or automatic programming.
  • Serial Port USB Uart Module Useful for debugging file transfer + USB kernel module file driver

Phase 2

  • Bank of 8 Configuration DIP Switches and LEDs (possibly via 3-8 encoders)

PCB Phyiscal Design

LPC Module sizes

Signal Values

From SCSI Programming Guide about OR-tied signals.

Signals can assume true or false values during information transfer. When a value is true, the signal is driven true, or asserted . When a value is false, the non-OR-tied signals are driven false, or negated , and OR-tied signals are released.

In this guide, whenever the term negated is used, it means that the signal is actively driven false, or simply released at the option of the implementor.

The advantage of actively driving signals false during information transfer is that the transition from true to false occurs more quickly and the noise margin is much higher than if the signal is simply released; this facilitates reliable data transfer at high rates.

See the ANSI SCSI-2 specification for additional information.

From Data Storage Fundamentals pg52 'Signal Drivers':

SCSI signals are either OR-tied or Non-OR-Tied.

The drivers do not drive OR-tied signals to the false state but instead use the terminator's bias circuitry > to pull the signal to a false state. Non-OR-tied signals may drive the signal to the false state.
Non-OR- tied drivers have the advantage of faster and cleaner signal transitions and provides for more reliable data transfers. The BSY, SEL and RST signals are OR-tied signals only.

Updated