Bt8370/8375/8376
2.0 Circuit Description
2.8 Transmitter
Fully Integrated T1/E1 Framer and Line Interface
2.8.2.2 PRM Generator
Performance Report Messages (PRMs) are HDLC messages containing path
identification and performance monitoring information. If automatic performance
report insertion is selected [AUTO_PRM; addr 0AA], a performance report is
generated each second and begins transmitting coincident with the 1-second timer
interrupt [ONESEC; addr 005]. The PRM is sent immediately if the processor
sets the SEND_PRM bit in the Performance Report Message register [PRM; addr
0AA]. All performance monitoring fields of the message are automatically filled
in when a PRM is generated. The remaining PRM bit fields are
application-specific and can be configured using the Performance Report
Message register.
For systems with a single processor and multiple Bt8370s, the automatic PRM
generation can off-load a significant portion of CPU bandwidth.
TBOP Transmitter
The Transmit Bit-Oriented Protocol (TBOP) transmitter sends BOP messages,
including ESF Yellow Alarm, which consists of repeated 16-bit patterns with an
embedded 6-bit codeword. The TBOP is configured to operate over the same
channel selected by Data Link #1 [DL1_TS; addr 0A4]. The TBOP must be
configured to operate over the FDL channel. This is required for TBOP to convey
Priority, Command, and Response codeword messages according to ANSI T1.403,
Section 9.4.1. The precedence of transmitted BOP messages with respect to
current DL1 transmit activity is configurable using the Transmit BOP mode bits
[TBOP_MODE[1,0]; addr 0A0]. BOP messages can also be transmitted during
E1 mode, although the 16-bit codeword pattern has not currently been adopted as
an E1 standard. The length of the BOP message [TBOP_LEN[1,0]; addr 0A0]
can be set to a single pattern, 10 patterns, 25 patterns, or continuous.
0xxxxxx0 11111111 (transmitted right to left)
[543210] TBOP = 6-bit codeword
BOP codewords are transmitted by writing to the Transmit BOP Codeword
[TBOP; addr 0A1]. The real-time status of the codeword transmission can be
monitored using TBOP_ACTIVE in the BOP Status register [BOP_STAT; addr
0A3]. A begin BOP transmit interrupt is available in Data Link 1 Interrupt Status
[ISR2; addr 009].
2.8.3 Sa-Byte Overwrite Buffer
Five transmit Sa-Byte buffers [TSA4 to TSA8; addr 07B to 07F] are available;
they insert Sa-bits into the odd frames of TS0. The entire group of 40 bits is
sampled every 16 frames, coincident with the Transmit Multiframe bit interrupt
boundary [TMF; addr 008]. Bit 0 from each TSA register is then inserted during
frame 1, bit 1 is inserted during frame 3, bit 2 is inserted during frame 5, and so
on, which gives the processor a maximum of 2 ms after TMF interrupt to write
new Sa-Byte buffer values. Transmit Sa-bits maintain a fixed relationship to the
transmit CRC multiframe. Each of the 5 Sa-Byte transmit buffers can be
individually enabled using the Manual Sa-Byte Transmit Enable in the Transmit
Manual Sa-Byte/FEBE Configuration register [TMAN; addr 074].
N8370DSE
Conexant
2-59
CONEXANT [ CONEXANT SYSTEMS, INC ]
