á
XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
274
NOTE: In
Figure 106, the unshaded boxes depict the tasks that the user must perform. The shaded boxes present the
resulting tasks that the Transmit HDLC Controller block will perform.
The Mechanics of Transmitting a New LAPD Message frame, if the LAPD Transmitter has been
configured to re-transmit the LAPD Message frame, repeatedly, at One-Second intervals.
If the LAPD Transmitter has been configured to retransmit the LAPD Message frame repeatedly at one-second
intervals, then it will repeatedly transmit the LAPD Message frame to the Remote Terminal Equipment at one
second intervals.
If another (e.g., a different) PMDL Message is to be transmitted to the Remote Terminal Equipment, this new
message will have to be written into the Transmit LAPD Message buffer, via the Microprocessor Interface block
of the Framer IC. However, care must be taken when writing this new PMDL message. If this message is
written into the Transmit LAPD Message buffer at the wrong time (with respect to these One-second LAPD
Message frame transmissions), the user’s action could interfere with these transmissions, thereby causing the
FIGURE 106. FLOW CHART DEPICTING HOW TO USE THE LAPD TRANSMITTER
E n ab le th e L A P D T ran sm itte r fo r
T ran sm is s io n
T his is d one by w riting the value 0000 0xx1b
into the T x D S 3 L A P D C on figuration R egister.
(xx dic ta tes the LA P D M es sage Len gth )
LA P D T ra nsm itter inserts F ram e H e ader
octets in fron t of the user p ayload.
Is
M essa ge
T ransm ission
Com plete
?
Are 5
C ons ecutive
"O n es" detected
betw een the
start and end flag
seq uence
?
ST A R T
NO
YES
NO
W rite in D a ta L in k In fo rm a tio n
T his is a ccom plis hed by w ritin g the info rm ation
to b e tra nsm itted via the LA P D T ran sm itte r to
locario ns, 0x 8A thru 0xD B in the F ram er
add res s s pace.
W rite th e H e a d er in 0x 86 to 0x89
Insert a "0" a fter
the string of 5
consecutive "1 's"
LA P D T ra nsm itter appe nds a F la g S e quenc e
T railer o cte t to the end of the LA P D
M essa ge after the 16 bit F C S .
LA P D T ra nsm itter com putes the 16 bit F C S
(a CRC-16 value) over th e He ader an d
P ayloa d b yte s a nd ins erts it in to the LA P D
M essa ge, follo wing the user p ayload.
EN D
G enerate Interrupt LA P D T rans m itter w ill
con tinue to transm it F lag S equenc e o ctets .
YES
In itia te T ran sm is s io n o f L A P D M essag e
T his is d one by w riting the value 0000 10x0b
into the T x D S 3 L A P D S tatus/Interrup t
R egister.
(x indictates th at th e u ser ca n c hoose to
ena ble /disa ble the LA P D M es sage T ransfer
C om plete Interrupt)