MT90812 Datasheet, PDF (37/105 Pages) Mitel Networks Corporation – Integrated Digital Switch (IDX)

Advance Information
MT90812
• The stop bit was not detected (RX stop bit error).
• The status of the received parity bit did not equate to the calculated parity (RX parity bit error).
12.0 Transmitter Operation
Fig. 23 illustrates the data flow for the D-channel data in the transmit direction. A system write to the TX FIFO
buffer is performed by addressing the “D-Channel TX FIFO Input (DTXIN)” register at location 44_HEX of the
Control Register page. Up to 32 bytes can be written to the FIFO. The output of the DBTX is memory mapped
to Data Memory location 70_HEX. The output of the Transmitter can then be directed to the specified output
channel by programming Connect Memory Low as 70_HEX for the intended output channel.
As with the Receiver, the Transmitter also operates in two modes: MLIM and FLIM. The TX control register “D-
Channel TX Control (DTXC)” at location 45_HEX of the Control Register page is used to program the Transmitter
for interrupt select, transmission rate at 1, 2, or 8 bits per frame, MLI or FLI mode, start and stop bit enable
(SE), parity enable (PE), and start transmission (ST). The transmission sequence starts when bit ST is set
followed by writing the first byte to the FIFO. The transmission bit order is determined from TXB0 bit in the “D-
Channel Receive Interrupt Threshold (DRXIT)” register. Refer to page 66 for a description on the transmission
bit order.
In MLI Mode, the Transmitter automatically appends the start and stop bits to an N byte message with an
optional parity bit. The status of SE bit has no effect on this mode but the PE bit specifies whether the message
to be transmitted requires a parity bit.
In FLI Mode, the status of SE and PE bits can provide three transmission methods. If the SE bit is disabled, the
Transmitter does not include start, parity and stop bits to the message regardless of the status of PE bit. If SE
is enabled, the user has the option of enabling or disabling the PE bit. The start, parity, and stop bits are
applied on a per byte basis.
The transmitted messages are always padded with stop bits for any remaining bits. For example in the case
where a byte long message is to be sent with start and stop bits and a data rate at 8 bits per frame, the
transmission of the message will take two frames and the stop bit will be in the second bit of the second frame
and the 3rd to 8th bits will be padded with stop bits.
The Transmitter operation also provides a message to be broadcast to several channels simultaneously. This is
accomplished by programming the Connect Memory of the intended outgoing channels all to 70_HEX. One
application for broadcasting messages might be to update displays on all phone sets.
Data Memory
70_HEX
Control Registers
Uport Write
44_HEX
DTXIN
DBTX
TX
TX FIFO
Output Stream
Parallel to Serial
Connect Memory
70_HEX
Channel m
Figure 23 - Data Flow for D-channel Transmitter
33