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An interface for Apple's LocalTalk networking protocol.
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README.md

TashTalk

Elevator Pitch

It's a LocalTalk interface, contained entirely within a single Microchip PIC12F1840 (8 pins, ~$1.50) microcontroller.

It handles all the time-sensitive aspects of LocalTalk, bidirectionally bitbanging the SDLC and FM0 (a.k.a. differential Manchester) based protocol at the data link and physical layers, sending and responding to control frames with CRC calculation and checking, and collision avoidance and retransmission. It can also respond to any number/combination of node IDs for use in bridging applications. It can be interfaced directly to user-mode software on a Raspberry Pi or BeagleBone or full PC, or it can be part of a larger embedded system. It slices, it dices, etc.

Project Status

Stable.

Caveats

Because of the PIC12F1840's limited memory and the way its UART is used, the host's UART needs to be able to handle a baud rate of 1 Mbps. Conventional UARTs don't expect to be pushed beyond 115.2 kbps. In addition, the PIC has a 128-byte receiver queue, which is considerably smaller than the largest possible LocalTalk frame (605 bytes). As such, the host needs to respect when the CTS hardware flow control line is deasserted so the queue doesn't overflow and be quick about resuming transmission when CTS is reasserted so the queue doesn't underflow either.

Also, "single-chip" doesn't include the separate and necessary driver/receiver chip for RS-422/485. Sorry. =)

Building Firmware

Building the firmware requires Microchip MPASM, which is included with their development environment, MPLAB. Note that you must use MPLAB X version 5.35 or earlier or MPLAB 8 as later versions of MPLAB X have removed MPASM.

PCBs and Products

End User Hardware

Serial Adapters

Software

  • tashtalkd by Tashtari
    • Simple LocalTalk (via TashTalk) to LToUDP bridge
    • Files
  • MultiTalk by sfiera
    • Bridge between EtherTalk and LocalTalk (via LToUDP and TashTalk)
    • Project page
  • TashRouter by Tashtari
    • Full-fledged AppleTalk router supporting EtherTalk and LocalTalk (via LToUDP and TashTalk)
    • Project page

Yours?

File a PR or an issue to add to these lists!

Version Comparison

AirTalk users: do not upgrade your TashTalk PIC to v2.x, it will stop working because of the change in pinout.

Version Pinout CRC Calculation
v1.0 RA3 input, RA5 output Self-generated frames only
v2.0 RA3 !MCLR, RA5 input/output Self-generated frames only
v2.1 RA3 !MCLR, RA5 input/output Self-generated frames, optionally all frames

UART Protocol

As of the time of this writing, the base UART protocol is unchanged between all available versions. v2.1 adds the "Set Features" command, but this can be ignored and is not used by tashtalkd.

Pinout Change in v2.0

This change was made in order to enable applications where it is desirable to disable LocalTalk and allow other circuitry to use the RS-422 driver - pulling RA3/!MCLR low will hold the PIC in reset, tristating its outputs. Using RS-422 interface ICs such as the SN65HVD series, RA5 can be connected to both the receiver output and the driver input while RA4/Driver Enable is connected to both the (active low) receiver enable and the (active high) driver enable.