IBM System/370 145 Reference Summary page 149

Byte Bit FTAG - 23 (IFA Only)
0 Set Cylinder Tag
1 Set Head Tag
2 Set Difference Tag
0
3 FTO Control Tag
4 CUA Load
5 Spare-A
6
Spare-B
7
Spare-C
(JK112)
0
128
1
64
2 32
1 3
FTI
16 -
Cylinder
4
8 Address
5
4 Register
6 2
7
1
(JK214)
0 128;
(Write Gate)
1
64;
(Read Gate)
2
32; Seek Start
2 3 FBO 16; Rst Head Req
4
8;
(Erase Gate)
5 4·
Select Head
6
2; Return to 000
7 1; Head Advance
(JK311)
0
-
1
-
2
-1
3 3 FDR
-
File
4
-
Data
5
-
Register
6
-
7 (JK411-412)
Ill
11.25