-------Station A ----------..., ",,-------- Station B ------- ....... , Main
Storage S/360 CPU X = Appl i cable Data Set/Modem
Synchronous
Feature X 2703 '00W& Information Path - Control Unit/Main Storage 8888888&§ Information Path - CPU/Main Storage
X
Sync hronous
Feature 2703 Figure 11. Operation of Two System/360 Computers over a Communications Line EBCDIC Translate Operation
via Translate E" E] t2 E3 E4 E5 E6 E7 (TR) Instruction Character Received from
v
Communication Facility 0 0 Bit positions in byte _
Character Transferred to 0 0 Main Storage Bit nome In byte- SBT 0 2 3 4 5
Character Received from EBCDIC Communi cation Faci lity !::. !::. 0 0 Translate
Tables
Character Transferred to 0 0 0 0 Main Storage Positions Filled
Bit Structure for this example is letter P !J. Unused data bit positions. EBCDIC, USASCII, ASCII-8, and SBT code charts are presented
in the pubiication "Generai information, Binary Synchronous Comrnunicotion". All codes from the line are received and assembled in the 2703. If the code structure is
fewer than eight data bits, it is right justified and transferred to its byte location in main
storage. Any missing bit positions in the main storage byte are filled. If the code received
from the iine has an 8-bit structure, it is transferred directly to its main storage byte location as in above examples. Figure 12. Code Translation of a Received Character (to EBCDIC or ASCII-8)
52
Main
Storage Channel :
___ -.J S/360 Main Storage 0 2 3 4 0 2 3 4 G 2 3 4 0 2 3 4 0 2 3 4 5/360 CPU 5 6
5 6
5 6
5 6
5 6
7 6 X 5 4 3 2 ..... - ., After trans I ation,
7 and X contain
same value. 7
7
7
7
7

Code-conversion operations
Source-program information
Groups of short messages
Object-program information
Encrypted data
Unedited information
Transparency is provided as a standard feature for EBCDIC and SBT. It is optionally available for USASCn. Transmission-Code Checking
The error-detection circuitry for each transmission
code is incorporated in the synchronous equipment.
Automatic-checking capability is provided for the
three transmission codes; however the checking
method employed depends on the Synchronous Ter­
minal Control and the kind of transparency chosen.
Table II indicates the checking methods available.
Table II. Transmission-Code Checking
Type of Checking
Transmission
No Transparency
Code
T ransparenc y Installed and Installed Operating EBCDIC CRC-16 CRC-16 USASCII VRC/LRC CRC-16 SBT CRC-12 CRC-12
CRC = Cycl ic Redundancy check
VRC = Vertical Redundancy check
LRC = Longitudinal Redundancy check
Transparency I nstalled But
Not Operating
CRC-16
VRC/CRC-16
CRC-12
VRC/LRC. This transmission-error-detection
method consists of a combination of the vertical
redundancy check (VRC) and longitudinal redundancy
check (LRC). Thus, an odd VRC parity check is
performed on each transmitted character including
the LRC character. The LRC check is an even
longitudinal check on the total data bits (not in­
cluding parity) of the transmitted block of characters
comprising the message block. The LRC is accumu­
lated at both the sending station and the receiving
station during the block transmission. This accu­
mulated value becomes the block-check character
(bcc). The trans mitted bcc is automatically
compared after ETX, ETB, or ITB with the bcc
accumulated at the receiving station for an equal
condition signifying correct receipt of the trans­
mitted block.
VRC/ CRC. This transmission-error-detection
method consists of a combination of a vertical
redundancy check and a cyclic redundancy check
(CRC). The CRC checking makes use of a circuit­
implemented polynominal that treats the transmitted
message as a binary nU!llber, and performs modulo
2 divide operations on this binary number (carries
are not considered). Both the sending and the recei­
ving stations generate this value individually. The
transmitting station sends its generated value
resulting from the modulo 2 division. Only the
remainder is transmitted to the receiving station, at
which point the two CRe values are compared. Equal
comparison indicates accurate transmission.
CRC. This checking method, as outlined above, be used in place of the other listed checking methods.
The two variations of the polynominal (CRC16 and
CRC12 for eight-bit and six-bit codes respectively)
are included in the publication, General Information-­
Binary Synchronous Communications, Form A27 -3004. Synchronous Bases
Three versions of Synchronous Bases are available: • Synchronous Base IA accommodates EBCDIC
or USASCII at speeds up to 2400 bps. • Synchronous Base IB accommodates SBT, USASCII, or EBCDIC at speeds up to 2400 bps. • Synchronous Base 2A accommodates EBCDIC or USASCII at speeds up to 4800 bps.
Synchronous Base 1A permits the attachment of up
to 24 lines using EBCDIC or USASCII terminal con­
trols and operating at bit rates not exceeding 2400 bits per second. This provides a character rate of
up to 300 characters per second [(2400/8) = 300 characters]. Up to 600 digits per second can be
transmitted in packed-decimal.
Synchronous Base 1B permits the attachment of up
to 16 lines using EBCDIC, USASCII, or SBT terminal controls and operating at bit rates not
exceeding 2400 bits per second. This provides a
character rate of up to 400 characters per second
[ (2400/6) = 400 characters] for SBT operation.
Synchronous Base 2A permits the attachment of up
to 12 lines using EBCDIC or USASCII terminal con­
trol and operating up to 4800 bps. This provides a
character rate of up to 600 characters per second (4800/8) = 600 characters or up to 1200 digits per
second in packed decimal.
Synchronous Line Set Synchronous communications facilities are attached
to the 2703, modular by four, via a Synchronous
Line Set. Each line set services up to four facilities
(half- or full-duplex). The maximum number of line
sets per Synchronous Base I depends on the trans-
mission code employed and whether the Synchronous
Clock feature is provided.
53