DC    X'1F',AL3(FILEMASK),X'40',x'00',AL2(1)         --- Set File Mask CCW
             :
             :
FIELMASK DC  X'file-mask-bits'

File Mask
00......  - Do not allow Write Home Address and Write Record Zero
01......  - Do not allow any write commands
10......  - Do not allow Write Format commands
11......  - Allow all write commands
...00...  - Allow all Seek commands
...01...  - Allow Seek Cylinder and Seek Head commands 
...10...  - Allow Seek Head commands
...11...  - Do not allow Seek commands or head switching
......0.  - Do not allow Diagnostic Write commands
......1.  - Allow Diagnostic Write commands
.......0  - Not PCI Fetch mode
.......1  - PCI Fetch mode
..0..0..  - Must always be Zero

   CCW Command     Normal  Multi-Track
Search ID Equal      31         B1
Search ID High       51         D1
Search ID Eq/High    71         F1

Search Key Equal     29         A9
Search KEY High      49         C9
Search KEY Eq/High   69         E9
 
Read Count           12         91
Read R0              16         96
Read Data            06         86
Read Key & Data      0E         8E
Read CKD             1E         9E
Read Multiple CKD    5E

Write CKD            1D         -
Write Data           05         -
Write Key & Data     0D         -

Erase                11         -

Set File Mask        1F         -

Track Size After Formatting = 19,254
Block Overhead w/No Key     =    185 (includes count area)
Block Overhead w/Key        =    267 (includes count area)