User`s guide

28 DC 900-1339H
FMP Programmer’s Guide
2.1.1 Bisynchronous Market Feeds
Most of the U.S. primary feeds use the bisynchronous (BSC) method of transmission to
broadcast data. BSC market feeds require the presence of a clock signal to receive the
feed. Clock signals are usually supplied externally by the synchronous modem. FMP
receives BSC-type framing when the line mode option is set to bisynchronous.
2.1.1.1 BSC 2780 Frame Structure
The BSC 2780 frame structure provides a method of transmitting individually block-
checked messages. Each data message is placed into a single record within the BSC
frame. Several records can be included in the frame until the specified maximum size of
the data frame is reached. The diagram below outlines the normal BSC 2780 text frame.
It begins with a start-of-header (SOH) character or a start-of-text (STX) character and
ends with an end-of-transmission-block (ETB) or an end-of-text (ETX) character. Each
data record within the text block ends with a unit separator character (US in ASCII, IUS
in EBCDIC), except the last record of the block. Each record is followed by a block
check character (BCC) that is a redundancy check (CRC-16 or LRC-8) of the characters
in that record, including the US or ETB/ETX character. The number of synchronization
(SYN) characters are described in Section 4.3 on page 70. PAD characters ensure com-
plete transmission of the data block.
SIAC’s Consolidated Tape System (CTS) and Consolidated Quote System (CQS), and
NASDAQ’s Level 2 are among the market feeds that use BSC 2780 framing.
2.1.1.2 BSC 3780 Frame Structure
When the BSC 3780 frame is used, data is broadcast with one message per block instead
of one message per record. The diagram below shows the normal BSC 3780 text block.
It begins with a start-of-header (SOH) or a start-of-text (STX) character and ends with
SYN SYN SOH record US BCC record US BCC record ETX BCC PAD