CAC 2020-04-18

T&D CIOC call

The T&D performs CIOC calls to channels 8 to 32. Each CIOC call is the same except for the channel number.
This is the data that the emulator sees on channel 12 (which is attached to the console):

["The book" is 43A239854 6000B EPS-1.]

The connect channel LPW contains:  001000040000

The book 3.21. "List Pointer Words" breaks this out:

bits
0-17   001000  DCW Pointer
18      1           RES   Restrict IDCW's and Changing AE flag
19      0           REL   IOM Controlled image of REL bit
20      0           AE      0: DCW is in first 256K
21      0           NC      0: Do not inhibit updating of DCW and TALLY fields
22      0           TAL     0: No Tally Runout or Pre Tally Runout indicators
23      0           REL    0: DCW address is absolute
24-35  0000   TALLY

Because this is the connect channel, the DCW pointer points to a PCW. The word pair is fetched from location 001000

pcw0 000000740000
pcw1 016000000000

The book 3.2.2 breaks this out as:

bits
0-11   0010   Channel information
12-17 00    Address extension
18-20  7    Must be 7
21     1    Mask
22-35  00000  Channel information

"The PCW is used by the Connect Channel to initiate the operation
of a channel, or to mask (turn off) the operation of a channel
that was previously initiated."

"A channel will change from the normal condition to a masked con-
dition as a result of a System Initialize, a system fault flag
from the IOM Central, or as a result of a PCW with bit 21 = 1.
This masked condition is a state in which a channel will not re-
quest service in spite of a need for such service that may be
generated in the channel. A channel will change from the masked
condition to normal as a result of a PCW with bit 21 = 0."

The emulator takes the words "a [masked] channel will not request service" strongly; this is interpreted to include Status Service. As soon as the Mask is is seen, the connect channel abandons the PCW interpretation and the CIOC is considered completed.

It would seem that the T&D tape expects some kind of response from a masked channel.