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1.22, MODEL 20 MODE
FEA~URE
The r.'bdel 20 mode feature is irr_t:lerrented
alrrost entirely ty microprograms.
It uses
the normal Model 25 CFU hardware and I/O
devices, exceft for the 2560 MFCM
attachment feature that can be added
Sfecifically for
~odel
20 mode operations
when required.
The rraintainal:ility plan for this mode
assumes that the CPU and all I/O devices
(except the 2560) are tested by the Model
25 diagnostics (resident and nenresident
rricrodiagnostics, and the System/360
macrodiagnostic tests).
~he
2560
attachment is tested ty nonresident
microdiagnostics, and the 2560 is tested ty
Irr_t:ulse Check Routines CICRs) and Medel 20
Machine Function Tests CMFTs).
Refer to
2025 MDM, Form Y24-3529, page 1-1.
The Model 20 Mode feature rricrefrograrrs
incorporate the following maintenance
features.
• Resident CPU microdiagnostic (BDIA) and
checksum tests,
• FE traf ( 64 tytes teginning at
control-storage address 0280),
• Resident card-reader microdiagnostic
(when the card reader is the enly infut
device).,
• Machine-check trap and 1052 lcgcut, and
• 1052 alter/display.
Operation of these rraintenance features
under Medel 20 Mode is the same as for the
basic 2025 except for rrachine check trai;:,
which is descrited in the following
section.
1. 22.1 l".ACHINE-CHECK TRAP ANC 1052 LOGOUT
With the check control switch set tc
PRCX::ESS, detection of rrachine check will
cause a machine- check trap to -be taken.
This microprogram stores status inf crrraticn
in a part of the protected first 144 bytes
of program storage.
This logout area is
also printed out on the 1052
frinter-keyboard.
The format of the logout
is identical to that presented fer Model 25
rrcde operation, and operation is similar
except that after the logout, the rrachine
step:; instead of initiating an interrupt.
(See Sections 1.11.1.1 and 1.17.1.2.)
1.22.2 DIAGNCSE INSTRUCTICN
The Diagnose instruction (Of-code 83) is
provided for use with the ICR and machine
function tests.
This instructicn can
ferform several functions as specified by
the Dl field of the instruction.
Fer
example, it is used to store the contents
of the six diagnose op switches (auxiliary
storage locations OOFC through OOFE) into
frogram storage at locations OOFC through
OOFE.
The diagnose instructicn permits a
diagnostic program to use special
diagnostic microprogram routines in
conjunction with normal rrachine
instructions.
A complete description of
diagnose actions is given in the 2560 test
descriptions, IDOOl in Vol.
44.
1. 22. 3 CE TRAP
With the diagnostic control switch in the
trap position, and any desired signal wired
into the CE test panel, a microprogram trap
is entered when the chosen signal goes
positive.
~is
function is the same for
Model 20 rrode as it is fer Model 25 mode.
1.22.4 CE TEST PANEL HUES
The function of the CE test-panel hubs
(sync, switching, and match) is the same
for
~odel
20 and Model 25 rr.edes Csee
Section 1. 2 3).
1 .• 22. 5 CE DISPLAY CABLE
This pluggatle service aid provides similar
information en the Model 25
o~erating
in
Model 20 mode as is provided on the Model
20 system.
The 2560 attachrrent feature
pluggatle display charts are included in
the publication, Model 25 External Field
Definitions, Forrr: 229-2176, available with
the CPU.
1.22.6 PROGRAMMING ERRORS
Prograroroing errors, such as invalid
op- code, addressing error, specification
error, etc., are detected by
microprograrorr:ing during execution of the
instruction.
on the Model 20, such errors
are indicated by stofping the system and
displaying an error code in the I-register.
However, when in Mode 1 20 rrode on the Model
25, the error code is printed on the 10 52
to provide a corresponding identification
of the error..
See MOM 5-604 for a summary
of error codes.
1. 22. 7 LOCAL S'IORAGE ZONE AND EXTERNAl MODE
FOR 2560
In 2020 mode (mode register bit 1 on), 2311
data operations cannot cverlap other
operations.
Therefore, local storage zone
1 is shared by the 2311 and 2560.
External
2025 FEMM (7/69)
1-127
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