13
SHM-768K
2.3.4 T
EST
P
ATTERN
G
ENERATOR AND
R
ECEIVER
This feature allows for easy and quick testing of the local modem as well as
the communication link. When the PATT button on the front panel is
activated, the circuit sends and checks a standard 511-bit pseudo-random
pattern. If errors are encountered, the ERROR LED remains ON or blinks.
The test pattern can be carried out in local analog loopback, in remote
digital loopback or in normal point-to-point operation opposite a remote
SHM-768K modem (press the PATT button on the remote unit or connect a
Bit Error Rate Tester that uses the standard 511 bit pattern).
2.3.5 X.21 B
UFFER
(
FOR
X.21
INTERFACE
)
To allow tail-end connection on an X.21 interface, a buffer is provided on
received data. When the SHM-768K is used in external clock configuration,
set Jumper X.21 EX.CK to EXT. When internal or receive clock configuration
is used, set the jumper to INT.
Figure 2-3. SHM-768K Block Diagram.
RTS
CD
RD
TD
ERROR
NRZ
NRZ
TIMING
GENERATOR
C0
CI
RXD
X.21
BUFFER
V.54
DELAY
REM
GENERATOR
REM
ANA
PATT
PATT
DIG
RTS
ANA
CTS
TXC
EXT
CLK
REM
TXD
CDP
DECODER
RXC
DCD
CLOCK
RECOVERY
CARRIER
DETECT
TRANSMIT LEVEL
ALB
CDP
ENCODER
RX
TX
EQUALIZER
AGC
GEN
BERT
TEST
