Register Descriptions (ESSI0_BASE = $1FFE20, ESSI1_BASE = $1FFE00)
MOTOROLA
Enhanced Synchronous Serial Interface (ESSI)
12-39
Preliminary
12
12.7.8.5 Transmit Enable 0 (TE0)—Bit 12
This control bit enables the transfer of the contents of the STX0 register to its Transmit
Data Shift Register 0 (TXSR0). TE0 is functional when the ESSI is in either Synchronous
or Asynchronous modes.
0 = The transmitter continues to send the data currently in TXSR0, then disables the
transmitter.
1 = On the next frame boundary, the transmit 0 portion of the ESSI is enabled. With
internally generated clocks, the frame boundary will occur within a word time.
If the TE0 bit is cleared, then set again during the same transmitted word, the
data continues to be transmitted. If the TE0 bit is set again during a different
time slot, data is not transmitted until the next frame boundary.
The serial output is tri-stated and any data present in the STX0 register is not transmitted.
For example, data can be written to the STX0 register with the TE0 bit cleared and the
TDE bit is cleared, but data is not transferred to the TXSR0.
The normal transmit enable sequence is to write data to the STX0 register or to the STSR
before setting the TE0 bit. The normal transmit disable sequence is to clear both the TE0
and TIE bits after the TDE bit is set. This bit should be cleared when clearing ESSIEN.
12.7.8.6 Transmit Enable 1 (TE1)—Bit 11
This control bit enables the transfer of the contents of the STX1 register to its Transmit
Data Shift Register 1 (TXSR1). TE1 is functional when the ESSI is in the Synchronous
mode. It is ignored when the ESSI is in the Asynchronous mode.
0 = The transmitter continues to send the data currently in TXSR1, then disables the
transmitter. The serial output is tri-stated and any data present in the STX1
register is not transmitted. In other words, data can be written to the STX1
register with the TE1 bit cleared, and the TDE bit is cleared but data is not
transferred to the TXSR1.
1 = On the next frame boundary, the transmit 1 portion of the ESSI is enabled for
that frame. With internally generated clocks, the frame boundary will occur
within a word time. If the TE1 bit is cleared and then set again during the same
transmitted word, the data continues to be transmitted. If the TE1 bit is set again
during a different time slot, data is not transmitted until the next frame
boundary.
When the TE1 bit remains clear until the beginning of the next frame, it causes the SC0
signal to act as a serial I/O flag from the start of the frame in both Normal and Network
modes.