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Optimized Bit Stream for IBM 5250 Protocol

IP.com Disclosure Number: IPCOM000119243D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 141K

Publishing Venue

IBM

Related People

Comp, CM: AUTHOR [+2]

Abstract

The IBM 5250 Information Display System protocol was designed for communicating with direct attached Work Stations (using twin-axial cable). It uses 16 bit frames, of which only half is data. This article describes how, after initial 16 bit frames, a block of data can be transmitted or received as 8 bit data frames. This can increase the data transfer rate to almost double the existing rate for block data transfers.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 47% of the total text.

Optimized Bit Stream for IBM 5250 Protocol

      The IBM 5250 Information Display System protocol was
designed for communicating with direct attached Work Stations (using
twin-axial cable).  It uses 16 bit frames, of which only half is
data.  This article describes how, after initial 16 bit frames, a
block of data can be transmitted or received as 8 bit data frames.
This can increase the data transfer rate to almost double the
existing rate for block data transfers.

      This article describes how data can be transferred as 8 bit
data frames after an initial one or two 16 bit frames. This can
increase the data transfer rate to almost double the existing rate,
for block data transfers, while maintaining the existing 1 Mbit per
second transmission rate.  This article allows existing 5250 type
W/Ss to coexist with W/Ss that utilize this new 8 bit frame
technique.  Two existing commands are used by the WSC to determine if
a W/S supports the 8 bit frames.  These are the Read Device ID and
Read Model ID commands sent from the workstation controller (WSC) to
the W/S after the W/S is powered on.

      The following describes how a block of data is transmitted to a
W/S using the new 8 bit frame technique. Items 1 through 4 are not
described in detail, but are included to show the steps involved with
transferring data. Item 5 describes the actual data transfer.
Sixteen bit frames are used for all of the commands.  The 8 bit
frames are only used for the block data transfer after the Write
Activate command.
1.   Load Address Command - sets the starting point in the W/S buffer
where data will be written.
2.   Escape Command - this command tells the W/S that a new command
follows.
3.   Optimized Write Data Command - this new command immediately
follows the Escape Command and notifies the W/S to use 8 bit frames
for receiving data after the next Write Activate is received.  The
Optimized Write Data command will be immediately followed by two 16
bit frames that contain a 16 bit byte count.  This byte count
indicates the number of data bytes to be transferred.  This is
required because, in 16 bit frames, the address field was used to
indicate end of transmission.  For 8 bit data frames, the W/S will
have to keep track of the byte count to determine the end of
transmission.
4.   Poll the W/S until the busy bit in the poll response goes
inactive.
5    Write Activate Command (see Fig. 1):
      a.   To allow existing and enhanced W/Ss to attach to the same
port, the first two frames sent will be 16 bit frames.  These frames
will have the format as indicated in Fig. 2.  The first 16 bit frame
will contain the 'write activate' command. The address part of the
frame contains the address of the W/S that will receive the data from
the WSC.
      b.   The second 16 bit frame will contain an 8 bit data byte.
This data byte is included in the byte count passed by the Optimized
Write Data command. Also, the address par...