IBM System/370 145 Manual page 28

Channel Masking Changes
When a System/370 operates in EC mode, interruptions from each
channel are controlled by the summary I/O mask bit (bit 6) in the
current PSW and an individual channel mask bi.t in control register 2.
In the Mode1 145, bits 0 to 4 in control register 2 are assigned to
control channels 0 to 4, respectively. Both the summary mask bit and
the appropriate individual channel mask bit must be on in order for an
interruption from a given channel to occur. In BC mode, interruptions
from channels 0 to 4 are controlled by only the channel mask bits (bits
o
to 4) in the current psw.
Expansion of Storage Protect Key Size
The size of the storage protect key associated with each 2K storage
block is expanded from five to seven bits when dynamic address
translation is present. The two additional bits (reference and change)
are included for use with dynamic address translation and are discussed
in Section 15:10. The
SET
STORAGE KEY instruction sets a seven~bit key
regardless of the mode, BC or EC, in effect. The INSERT STORAGE KEY
instruction causes a five-bit or a seven-bit key to be loaded into the
register indicated, depending on whether BC or EC mode, respectively, is
in effect.
Chanqes to Certain System/310 Instruction Definitions
All Model 145 instructions are valid in BC and EC modes. However,
because of the differences between the PSW format and the permanently
assigned storage locations in EC and BC modes, the definition of certain
instructions is affected. Instructions provided for both System/360 and
system/370 whose definition is altered for EC mode are:
BRANCH
AND LINK (RR, RX)
INSERT STORAGE KEY
LOAD PSW
SET
PROGRAM
MASK
SET STORAGE KEY
SET SYSTEM MASK
SUPERVISOR CALL
Revised definitions of these instructions to include BC/EC mode
differences are contained in system/310 Principles of Operation (GA22-
1000-2 or later editions). Programs that operate in BC mode and that
use LOAD PSW and/or SET SYSTEM MASK (SSM) instructions must be modified
in order to operate correctly in EC mode. The eight-byte PSW to be
loaded by LPSW instructions and the eight-bi.t system mask to be set by
SSM instructions must be changed to EC mode format. (Programs that use
SSM instructions and that are to be executed in an OS/VS1 or OS/VS2
environment need not be so modified because the interruption for SSM
instructions and an SSM simulation routine, described next, are
supported. )
Programs that use the other instructions listed do not have to be
changed in order to operate correctly in EC mode unless they use other
facilities that are mode dependent. Programs that operate in Be mode
and that use the STORE THEN OR SYSTEM MASK and STORE THEN AND SYSTEM
MASK instructions (not provided for System/]60) must also be modified in
order to operate correctly in EC mode.
18 A Guide to the IBM System/310 Model 145