Specifications

58 Telephone Interface
This separation makes it possible to have TLI assemblies that are not
mounted in the Q-bus IO connector panel. If there is any length of
cable between the TLI assembly and the module, it is necessary to have
separate send and receive data wires. The two wires are called TX DATA
H and RX DATA H (Table 4-1). The module sends data to the TLI over
the TX DATA H line. The TLI sends its identification code and other data
to the module over RX DATA H.
If the TLI assembly is mounted in the Q-bus IO connection panel, only
one wire is needed for moving data between the module and TLI. In this
case, the standard bidirectional SLD data is sent over the single TX DATA
H line. The module uses the ONE WIRE L signal to determine whether
one or two data wires are needed (Table 4-1).
4.1.2.2 Identification Data Byte
On a single board, the SLD chips that represent the master and the slave
devices are always the same. In this case, it is not necessary for the
master to identify itself to the slave.
In the DECvoice system, the master and slave devices are on separate
boards. It is possible that the master and slave devices could have
different programming requirements. Therefore, the TLI must send a
byte of identification data to inform the DTC04 module what is at the
other end of the cable. The identification byte informs the module of the
following:
• What type of SLD chip the TLI is using (a 29C49, 29C50, 29C52, or
some other chip)
• The exact meanings of the bytes in the data frames over the SLD
slave and SLD master lines
• Any legal restrictions the microcode driving the interface must follow
The TLI sends the identification byte to the module when the module
sends its first byte of data to the TLI.
4.1.2.3 Reset Line
When all components are on the same board, the power-up voltages all
sequence at the same time. It is not necessary to synchronize a reset
operation between components on the board, since all components receive
power at the same time.
In the DECvoice system, the SLD master and slave devices are on
separate boards. In this case, it is necessary to synchronize reset
operations between the module and the TLI. A reset line has been added
between the module and TLI assembly called TLI RESET. When the
module resets, it asserts TLI RESET so that the TLI also resets.