MT90812 Mitel Networks Corporation, MT90812 Datasheet - Page 45

• Manufacturer Part Number: MT90812
• Description: Integrated Digital Switch (IDX)
• Manufacturer: Mitel Networks Corporation

Advance Information
In multiplexed operation, the receiver obtains the next RX channel (NRX) number from the RX channel Auto-
hunt circuit. Three conditions must be met before the RX circuitry will initiate receiving a packet:
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The order in which these three conditions are satisfied is not important. For the first condition to be true the
Auto-hunt circuit must detect the RTS pattern '01111110' on the current D-channel
The second condition is met by setting the status bit (RXCHNL) high in HRA Status 1 (HS1) register when a
new receive channel number is latched. This disables subsequent receive channel number latching until the
system clears that bit by reading PRX in HRA Status 3 (HS3) register. If the system wants to stop the HDLC
receiver, it may do so by not reading PRX.
The third condition, that the HDLC receiver be inactive, is achieved by the detection of a receive end-of-packet
strobe (REOP) from the HDLC controller chip.
At the start of the reception of a packet the following five actions are taken:
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14.1.5
Clear-to-Send Active (CTSACT) is in HRA Status 1 (HS1) register. CTSACT set high indicates that the receiver
is currently transmitting a clear-to-send go-ahead pattern to the peripheral on the transmit channel denoted by
PRXi. The CTS pattern generated is the 9-bit HDLC go-ahead character '011111110' (7F +’0’). For a 16k baud
rate, this bit pattern is sent out 2 bits/frame in the appropriate D-Channel. When the go-ahead is complete,
CTSACT will be forced low, and control of the particular D-Channel used for the go-ahead transmission will be
returned to the system.
The CTS generator can be re-triggered by the system, if desired, by setting the Re-initiate Clear To Send
(RECTS) bit in “HRA CTRL Register 2 (HC2)” on page 71. Once a new CTS pattern has been initiated, the
RECTS control bit will automatically be cleared by the RX circuitry. RECTS is acted upon with the same timing
as the normal source of CTS initiation.
14.1.6
There are four conditions which will cause the Auto-hunt circuit to stop monitoring a particular channel for flags.
They are:
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The first, which was described above, is when a flag has not been detected within 15 valid bit times.
The Auto-hunt circuit must have detected a request-to-send (RTS) flag.
The system must have read the channel number for the most recently active receive channel. This
condition is not required if the received RTS flag is the first detected flag after reset.
The receiver must currently be inactive.
the NRX channel number will be latched into the PRX (present receive channel) bits, where it will define
the active receive channel time;
an internal receive-active flag (RXACT) will be set, allowing RxCEN to be enabled during the
appropriate channel time;
the RXCHNL status bit will be set, to inform the system that a new PRX channel number is available;
the Auto-hunt circuitry will be cleared, and forced to move on to the next channel to be scanned;
and a CTS go-ahead pattern will be initiated (CTSACT high).
RTS is not detected
the channel is the current active receive channel
the channel is locked out
the channel is the current active transmit channel
CTS Generation
Circumstances When Monitoring a Channel is Stopped
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