• I IOpera- ICommand I I ITP Opl I Ition I Code IAddress IFlagslCode ICount 1--------------------------------------- I D i s-I' 2F' 0 lable ILine CC, I SILl 1 I 01 1
1--------------------------------------- ISet 1'23' 1'40' CC, I 01 1 !Mode SILl, 1------------------------------------------ IEnablel 1'27' 0 SILl I 01 1 ILine 1 I 1 IOpera-ICo •• andl I ITP Opl I Ition 1 Code IAddress IFlagslCode ICountl 1--------------------------------------1 I Dis- I' 2F' 0 SILl I 01 1 1 lable I I ILine I I , After a line is enabled, communication can then be directed to a
particular resource. The sequence of events (for a write disable and
write continue) is as follows: Send a data link control character on the line that places the
control unit in control .ode. This .ode makes the control unit
receptive to the specific address indicated by the second CCI. The
third CCI is a read CCI that is needed for the acknowledge.ent response from the addressed control unit. Normally, in response, CP trans.its a
block of data to that device with a write text CCI. Acknowledgement of
receipt of this data is contained by the read response (write continue) eel. The format of the CCI write initial and write continue operation
follows. !rite !nit!g.! I Opera-ICo •• and I I ITP Opl I tion I eode IAddress IFlagslCode I Count Write I 01 Table ce, I 02 1
an EOTI SILl I Write I 01 List ee, I 03 ILIST ad- I SILl I I dress-I I I ing I I I char. I I I Read 02 IResponse I SILl I 05 2
Re- I I I I I sponse I I I I I 1-100 IB! VM/370 System Logic and Problem Deteraination--Volume 1

I IOpera-ICommand I I I ITP Opl I Ition I Code IAddress IFlagslCode ICountl 1-------------------------------------1 IWrite 01 Area CC, I 10 Ivari-I Itext SILII lable I I 1 IRead 02 IResponsel SILl I 11 2 I IRe- I I I I I I sponse I I I I I , I In situations where the line is found to be in text mode, CP can
issue a write reset sequence to put the binary synchronous line in
control mode. The following format illustrates the write reset CCI. I , IOpera- ICommand I I ITP Op I I Ition I Code IAddress IFlagslCode ICountl I I I Write 01 Table SILl I 09 1 I I EOT I I In situations where the expected response from a remote station was not received or was invalid, the channel program may request the remote
station to retransmit the response. The following write ENQ for.at
shows this sequence. The remote station, upon receipt of the ENQ message, responds by transmitting the expected or valid response to the
response area indicated by the second CCI. • Opera-ICommandl I ITP opt I tion I Code IAddress IFlagslCode ICountl ----------------------------------------1 Write 01 ENQ I Table I CC, I 03 SILl I 1 I I --------------------------------------1
Read 02 Re- I sponsel IResponse I SIL! 1 11 I I I I I I 2 I I I ,
Read operations occur following a general poll or a specific poll for
text messages. In a general poll sequence, CP transmits the general
poll characters to the attached control unit on the bisync line. The
control unit recognizes the polling request, then the list (referred to
in the poll CCW) of enabled devices is scanned for any messages that are
queued and ready for trans.ission. 1 positive acknowledgement (yes, I
have a message to trans.it) from any of the attached devices causes the
next ccw to be skipped. The last CCI provides the read buffer and the
count necessary for the incoming data block from the first remote CP Introduction 1-101