High when calling. Could be off-hook signal. Enable external mike and speaker, connect to GND to do so. Enable external mike and speaker, connect to GND to do so. All signals seem to be at 5V logic.
Most debug messages are text.
Query battery level Interfacing circuitry TTL signal levels are use on the data pins of the GA628. CR Carriage return is forbidden by the TAP protocol and cannot be included in the message text. The option Menu size turns up Choose 'yes' and go from there. An alarm clock turned up too but it never rang. I think this was because there is no clock in the phone.