Specifications

56 Telephone Interface
SDIR
The SDIR signal controls the direction of transmission over the SLD line.
When the SDIR line is asserted, the SLD line transfers data to the slave
device. When the SDIR line is not asserted, the SLD line transfers data
to the master device.
SLD
The SLD line is the data line for the system. The SLD line supports a
512 Kbits/s rate, as defined by the SCL clock signal. The data on the SLD
line is formatted as 32 bits of receive data (towards slave) followed by 32
bits of send data (from slave). This pattern repeats at an 8 kHz rate. The
transmit and receive data is further divided into eight bytes, four for each
direction with the most significant bit first. The devices connected to the
SLD line determine the exact use of it.
For analog subscriber lines, the four bytes of data per direction are the
following:
• Primary voice—This byte contains the actual voice data transferred
between DECvoice and the telephone network. This byte is the
primary voice path.
• Secondary voice—This byte can have various uses, depending on the
system. This byte is often used as an extra voice channel for three-
way calling. This byte also lets one SLD line serve two telephone
lines. DECvoice can use either the primary voice byte or secondary
voice byte for data exchange, but not both.
• Control—This byte is used to program the Intel SLD components,
specifically the Intel 29C50 chip.
• Signaling— This byte controls network relays and reads the ring and
line current detection signals.
For digital subscriber lines, there are two voice (or data) bytes, a control
byte, and a signaling byte. The voice bytes can be used as one voice
stream and one data stream, two voice streams, or two data streams.
DECvoice only supports the use of one data byte as a channel to exchange
data.