station on the list that had a message queued for transmission. If,
however, all remote stations respond with negative acknowledgement (no messages queued) or any station queried for a response fails to respond,
then the channel program ends with the third CCW. The following read init{al format shows the initial read CCW sequence.
r IOpera- ICommand I I ITP Opl ItioD I Code IAddress IFlagslCode ICount I IWrite 01 Table CC, I 02 1 I EaT SILl I I IPol1 09 List CC, I 03 ILIST I SILII I I !T/O 0 ! 07 1 INo- I lopera-I Ition I I IRead 02 Area SILl I 10 162 IText I I After CP receives a message from a remote station, it .ay reissue the
initial read sequence to poll the remaining stations on the list (assuming the list of enabled devices was not exhausted on the first
pass of the initial read sequence). In the event that the list was
exhausted on either the first or a subsequent initial read sequence, CP starts the poll delay, then allows the poll delay interval to expire
before starting another read scan to the line (assuming CP has no higher
line priority tasks to process). If, in the process of receiving
aessages froa remote stations, CP receives a message block that is
invalid or its beginning or ending bisync control characters are not
recognized, CP can elect to send a negative response back to the reaote station. This negative response, the NAK control character, causes the remote station to retransmit the previous message to CPt this incoming aessage is processed by the second CCW of the read repeat sequence as
shown in the format below. I I IOpera-ICommand I I ITP Opl I Ition Code IAddress IFlagslCode ICount I I I IWrite 01 Table CC, I 06 1 I I NAK SILII I I I IRead 02 Area SILl I 10 162 I IText I I , I Once CP message processing receives an error-free aessage fro a a reaote station, CP sends an RVI control character to the remote station
before processing the message. The remote station, upon recognition of
the RVI character, halts the sending of additional queued data and
responds with EaT (instead of the noraal lCKO/1CK1 response). The 1-102 IBK VK/370 System Logic and Problem Deter.ination--Voluae 1

second CCW of the read interruption sequence processes the EOT response
from the remote station as shown in the for.at below • Read I • IOpera- ICommand I I ITP Op I I Ition I Code IAddress IFlagslCode ICountl I I IWrite xt 01' I Table CC, I 06 2 I I RVI I SILII I I I IRead X'02' IResponse I SILl I 11 2 I IRe- I I I I , Isponsel I I 1 I ,
DATA FORMATS - BISYNCHRONOUS LINES AND REBaTE 3270s CP, in conjunction with remote 3270 support, uses the following formats for its text messages. For a detailed explanation of the abbreviations
used, see the 327Q Information Display CoaponentDescription.
Display commands use this message format for the placement or erasure of
data anywhere on the display screen.. The display co •• ands that implement this function are: WRITE (X'F1'), ERASE/WRITE (X'F7') and COpy (X'F7') • rl----------------------------------------------------------//----------- ISTXIESCICMDIWCCIBSAI Buffer larders ISBAI Buffer ETI IAddress I & Text I I Address
1 1 1 1 1 2 variable 1 2 1
The COpy command is limited to compatible printers located on the same control unit. Action starts by pressing a PF key designated for the COpy function. CP responds by sending a message to the control unit
that contains both the designated printer and the display station that
requested the action and directs the control unit to print the
designated display buffer to the printer specified.
The format of the COpy messages follows:
CP Introduction 1-103