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XRT72L52
467
REV. 1.0.3
TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
Pull the Snd_Msg input pin "High" to transmit data via the Transmit HDLC Controller block. Once the Snd_Msg
pin is pulled high, then the Transmit HDLC Controller block will begin to sample the data on the
TxHDLCDat[7:0] input pins upon the falling edge of the TxHDLCClk clock output signal. Each byte of data that
is sampled and latched into the Transmit HDLC Controller block will be encapsulated into an outbound HDLC
frame.
After the last byte of data has been latched into the Transmit HDLC Controller block, then the user must pull
the Snd_FCS input pin "High" for either two or four TxHDLCClk clock periods.
If the user has configured the Transmit HDLC Controller block to append a 16-bit CRC value (from here on,
referred to as CRC-16); then the user must pull and hold the Snd_FCS input pin "High" for two (2) TxHDLCClk
clock periods. Conversely, if the user has configured the Transmit HDLC Controller block to append a 32 bit
CRC value (from here on, referred to as CRC-32); then the user must pull and hold the Snd_FCS input pin
"High" for (4) TxHDLCClk periods.
Pulling the Snd_FCS input pin "High" configures the Transmit HDLC
Controller to begin its insertion of either the CRC-16 or CRC-32 value into the back-end of the outbound HDLC
Controller.
An abort sequence may be transmitted by setting Snd_FCS “High” while Snd_MSG is set “Low”.
TxHDLCClk
O
Transmit HDLC Controller Clock Output signal:
This output signal functions as the demand clock for the Transmit HDLC Controller. When the
user pulls the Snd_Msg input pin "High" then the Transmit HDLC Controller block begins to
sample and latch the contents of the TxHDLCDat[7:0] upon the falling edge of this clock sig-
nal. The user is advised to configure their terminal equipment circuitry to output data onto the
TxHDLCDat[7:0] bus upon the rising edge of this clock signal.
Since the Transmit HDLC Controller block is sampling and latching 8-bits of data at a given
time, it may be presumed that the frequency of the TxHDLCClk output signal is either
34.368MHz/8 or 44.736MHz/8. In general, this presumption is true. However, because the
Transmit HDLC Controller is also performing “0” stuffing of the user data that it receives from
the Terminal Equipment, the frequency of this signal may be slower.
TxHDLCData[7:0]
I
Transmit HDLC Controller - Input Data Bus:
These eight input pins function as the byte-wide input interface to the Transmit HDLC Control-
ler. If the user pulls the Snd_Msg input pin "High", then the Transmit HDLC Controller block
begins to sample and latch the contents of this data bus into the Transmit HDLC Controller
circuitry upon the falling edge of TxHDLCClk. All data that is sampled via this byte-wide inter-
face will ultimately be encapsulated into an outbound HDLC Controller.
LSB of the TxHDLCData[7:0] is transmitted first.
If the user pulls the Snd_Msg input pin "Low", then the Transmit HDLC Controller block will
ignore the data that is being applied to this data bus.
TABLE 98: DESCRIPTION OF EACH OF THE TRANSMIT HDLC CONTROLLER PIN
PIN NAME
TYPE
DESCRIPTION