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68 lines
3.2 KiB
Markdown
68 lines
3.2 KiB
Markdown
TashTalk v1.x Prototype Details
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===============================
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Raspberry Pi
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A Raspberry Pi 3 Model B was used. Note that these instructions are specific to this model and may differ for other models.
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### UART Setup
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#### raspi-config
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Under `Interface Options` > `Serial Port`, answer "No" to "Would you like a login shell to be accessible over serial?" and then "Yes" to "Would you like the serial port hardware to be enabled?".
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#### /boot/config.txt
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Add the following lines:
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* `dtoverlay=miniuart-bt`
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* Ordinarily, the Bluetooth device uses the PL011 UART (/dev/ttyAMA0); this line forces it to use the mini-UART instead. We want the PL011 UART available because it's the only one that supports hardware flow control.
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* `gpio=16-17=a3`
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* This line switches GPIO16 and GPIO17 to be CTS and RTS for hardware flow control.
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### Connections
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| PIC12F1840 Pin | RPi 3 Pin |
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| -------------------- | ------------- |
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| 01 Supply | 01 3v3 Power |
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| 02 RA5/LocalTalk Out | |
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| 03 RA4/Driver Enable | |
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| 04 RA3/LocalTalk In | |
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| 05 RA2/UART CTS | 36 GPIO16/CTS |
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| 06 RA1/UART RX | 08 GPIO14/TXD |
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| 07 RA0/UART TX | 10 GPIO15/RXD |
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| 08 Ground | 06 Ground |
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Driver/Receiver
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---------------
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While the LocalTalk bus is half-duplex, LocalTalk and PhoneNet dongles use a hybrid transformer to accommodate the SCC's separate TxD and RxD lines. Because a PhoneNet dongle was used for the prototype, a pair of SN65HVD08 were used, one as a receiver and one as a driver.
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Other RS-422/485 drivers may be suitable, but it is important to experimentally verify that their receivers output a logic '1' when the bus is not being driven.
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### Connections
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| Receiver SN65HVD08 Pin | PIC12F1840 Pin | LocalTalk/PhoneNet |
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| ---------------------- | -------------------- | ------------------ |
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| 01 R | 04 RA3/LocalTalk In | |
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| 02 !RE | 08 Ground | |
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| 03 DE | 08 Ground | |
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| 04 D | | |
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| 05 GND | 08 Ground | SGnd |
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| 06 A | | RxD+ |
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| 07 B | | RxD- |
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| 08 Vcc | 01 Supply | |
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| Transmitter SN65HVD08 Pin | PIC12F1840 Pin | LocalTalk/PhoneNet |
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| ------------------------- | -------------------- | ------------------ |
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| 01 R | | |
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| 02 !RE | 03 RA4/Driver Enable | |
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| 03 DE | 03 RA4/Driver Enable | |
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| 04 D | 02 RA5/LocalTalk Out | |
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| 05 GND | 08 Ground | SGnd |
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| 06 A | | TxD+ |
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| 07 B | | TxD- |
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| 08 Vcc | 01 Supply | |
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