SCSI2SD Schematic Notes: Difference between revisions
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Details for the circuit design of [[SCSI2SD]]. | Details for the circuit design of [[SCSI2SD]]. | ||
== SMT Type == | |||
# 0805 sized components will be used where applicable. These represent a good tradeoff between hand-solderability and PCB board space. | |||
== Crystal Oscillator == | == Crystal Oscillator == | ||
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Where CL is the crystal's load capacitance, as specified by the crystal manufacturer, and CS is the PCB's stray capacitance (around 5pF for a reasonable PCB). | Where CL is the crystal's load capacitance, as specified by the crystal manufacturer, and CS is the PCB's stray capacitance (around 5pF for a reasonable PCB). | ||
== 3.3V | [http://au.element14.com/txc/9c-25-000meej-t/quartz-crystal-25-mhz-18-pf-hc/dp/1842314 TXC - 9C-25.000MEEJ-T] Load capacitance 18pF. Therefore, use 2x 22pF standard ceramic capacitors. | ||
== Power Supply == | |||
5V supply from hard drive molex connector will provide more than sufficient current. | |||
3.3V current requirements: | |||
# LPC1751: Rated at 100mA per supply pin, 4 I/O power pins, 2 core power pins, 1 analog supply pin = 700mA. | |||
# SD Card: 100mA | |||
5V power requirements: | |||
# SCSI terminator: 440mA (optionally powered by SCSI TERMPWR) | |||
# 74HCT05: ?? Not much | |||
Linear LDO: Simple, but may get hot | |||
Switching: Less heat. | |||
== In-circuit programming == | == In-circuit programming == | ||
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Custom header ? | Custom header ? | ||
Custom bootloader as well ? | Custom bootloader as well ? | ||
Reuse for serial debug output ? | |||
== Switches == | == Switches == | ||
TERMPWR, terminator, parity, SCSI ID | TERMPWR, terminator, parity, SCSI ID | ||
Revision as of 12:45, 7 October 2011
Details for the circuit design of SCSI2SD.
SMT Type
- 0805 sized components will be used where applicable. These represent a good tradeoff between hand-solderability and PCB board space.
Crystal Oscillator
- LCP1751 requires a 25MHz crystal, which results in a 100MHz clock with x4 PLL
- The crystal requires 2 caps for stability. The required value is:
2 * (CL - CS)
Where CL is the crystal's load capacitance, as specified by the crystal manufacturer, and CS is the PCB's stray capacitance (around 5pF for a reasonable PCB).
TXC - 9C-25.000MEEJ-T Load capacitance 18pF. Therefore, use 2x 22pF standard ceramic capacitors.
Power Supply
5V supply from hard drive molex connector will provide more than sufficient current.
3.3V current requirements:
- LPC1751: Rated at 100mA per supply pin, 4 I/O power pins, 2 core power pins, 1 analog supply pin = 700mA.
- SD Card: 100mA
5V power requirements:
- SCSI terminator: 440mA (optionally powered by SCSI TERMPWR)
- 74HCT05: ?? Not much
Linear LDO: Simple, but may get hot Switching: Less heat.
In-circuit programming
UART0 pins, + active low program enable power supply while programming ? Custom header ? Custom bootloader as well ? Reuse for serial debug output ?
Switches
TERMPWR, terminator, parity, SCSI ID
