2.0 Circuit Description
2.4.6 Test Pattern Receiver
The test pattern receiver circuitry can sync on framed or unframed PRBS patterns
and count bit errors. This feature is particularly useful for system diagnostics,
production testing, and test equipment applications. The PRBS patterns available
include 2E11-1, 2E15-1, 2E20-1, and 2E23-1. Each pattern can optionally
include Zero Code Suppression (ZCS).
The Receive Test Pattern Configuration register [RPATT; addr 041] controls
the test pattern receiver circuit. BSTART control bit (in RPATT) must be active to
enable the test pattern receiver and to begin counting bit errors. RPATT controls
the PRBS pattern, ZCS setting (ZLIMIT), and T1/E1 framing (FRAMED).
RPATT selects which PRBS pattern the receiver should hunt for pattern sync.
ZLIMIT selects the maximum number of consecutive zeros the pattern is allowed
to contain. FRAMED mode informs the PRBS pattern receiver not to search for
the pattern in the frame bit in T1 mode or search for the pattern in time slot 0 (and
time slot 16 if CAS framing is selected) in E1 mode. CAS framing is selected by
setting RFRAME to 1 in the Primary Control register [CR0; addr 001]. If
FRAMED is disabled, the PRBS pattern receiver searches all time slots for the
The RESEED bit in RPATT informs the receive PRBS sync circuit to begin a
PRBS pattern search. Once the search begins, any additional writes to RESEED
restarts the pattern sync search at a different point in the pattern. The time to sync
depends on the pattern and number of bit errors in the pattern.
Pattern sync is reported (when found) in PSYNC status of the Pattern Interrupt
Status register [ISR0; addr 00B]. After pattern sync is found, the PRBS Pattern
Error counter [BERR; addr 058 and 059] begins counting bit errors detected on
the incoming pattern, provided that BSTART remains active. Error counting stops
if the BSTART bit is cleared. BERR counter is reset to 0 after every read, or
latched on every ONESEC interrupt as selected by LATCH_CNT [addr 046]. An
interrupt is available to indicate the BERR counter overflowed in ISR4.
Fully Integrated T1/E1 Framer and Line Interface