Prosody data communications Protocols: TTY rx

TTY is a teletypewriter, or teleprinter. In this case specifically a telecommunications device for the deaf (also known as a TDD) which uses ITU V.18 Annex A coding at either 45.45 or 50 baud. This is often referred to as "Baudot" code. It has no configuration options.

API function behaviour

This should be read in conjunction with the generic data communications documentation.

smdc_channel_config()

You must use #include "smdc_ttyrx.h" to get the appropriate declarations.

The protocol value is kSMDCProtocolTTYrx.

There is no configuration for this protocol, so the config_data pointer should be null (0) and the config_length should be zero.

This protocol does not use encodings, so the 'encoding' field must be set to the value kSMDCConfigEncodingNone.

The firmware module ttyasyrx must have been downloaded.

smdc_line_control()

[note] not useful - receiver is always connected.

smdc_line_status()

smdc_tx_status()

This function is not applicable since it only applies to the output half of a channel.

smdc_tx_control()

This function is not applicable since it only applies to the output half of a channel.

smdc_rx_status()

When the returned status is kSMDCRxStatusCarrier the carrier value is an estimate of the duration of the bits being received in milliseconds.
Note there is no tracking of carrier on/off.

smdc_rx_control()

The kSMDCRxCtlResume command changes the symbol decoder mode. If blocking is zero it puts the symbol decoder into Letters (LTRS) mode until the next Figures (FIGS) mode symbol is received, otherwise it puts the symbol decoder into Figures (FIGS) mode until the next Letters (LTRS) mode symbol is received.

smdc_rx_data()

The data consists of bytes containing ASCII characters decoded from the received 5 bit symbols, and indicators showing when the decode mode has changed. These are 0xff for the change to LTRS and 0xfe for the change to FIGS.

smdc_tx_data()

This function is not applicable since it only applies to the output half of a channel.