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ADDRESS ERROR DETECTION
•
An invalid 1400 character (SF) is
placed in 1401 address 000 minus 1
for error detection4
•
2030 circuits detect a storage wrap
error4
. R 3 bit on signifies and invalid
address character4
Because the high-order position of
the 1400 system storage is physically
the same location as the high-order
position of 2030 memory, 1400 systems
storage wrap errors are detected in the
2030 through existing error detection
circuits 4
To detect an error when
address 000 is modified by minus one, an
invalid character has been placed in
2030 memory one core location below the
address assigned to 1400 storage loca-
tion 000.
If this location is
addressed, the invalid character causes
a wrap trap that initializes the halt
routine.
The invalid character is
placed in storage by the 1401 initializ-
ing program that loads local storage and
puts the machine into compatibility
mode.
When converting 1400 system addresses
to 2030 addresses, another error detec-
tion device detects invalid characters
in the address4
When the micro program
converts a 1400 system address to a
binary address, it is done in three
stages.
First, the hundreds digit is
used to address the table and a binary
equivalent is extracted.
Next, a binary
equivalent of the tens digit is extract-
ed and added to the hundreds value.
Finally, the units digit is obtained and
added to the total of the tens and
hundreds already obtained.
When the
hundreds digit addresses local storage
to obtain a binary equivalent, the tens
and units of the address are disregarded
and assumed to be zero.
(ie: 5 in the
hundreds position brings out the binary
equivalent of 500 plus bias).
When the
tens digit addresses local storage for
conversion, the units position is
assumed to be zero.
Since the tens and
hundreds digits extract binary values
that are round numbers (numbers that end
in zero), the 1 bit is not turned on.
To provide for error detection the hexa-
decimal values in the conversion table
for the tens and hundreds have been
crossed.
An example is : the tens 2
(20) equivalent in hex is 1 4, but it is
stored in local storage as 4 1.
When 4 1 is read out of local
storage, the R-register 3-bit (R3) is
not turned on.
Note also that the
units, 0-9 if not crossed, will never
turn on R3.
Therefore, when addresses
are read out, if R3 is on, it is an
invalid address.
Observe the local
storage map for compatibility mode anJ
note that all invalid digit values in a
1400 system address turn on the R3 bit
when they are read out (Figure 5-5) •
OP COD.E RECOGNITICN
•
1400 system Op codes are convert- to
bit significant characters.
•
Op code conversion table is stored
in local storage.
•
1400 system Op code character bits 0
and 1 are forced on before using the
character to address the conversion
table.
•
Converted Cp code is stored in the
G-register during I cycles.
1400 system Op codes in their EBCDI
configuration would require extensive
interrogation by the micro program to
determine exactly what the Op code is,
since their EBCDI bit configurations
would not readily indicate what type of
Op code the machine is handling_
To
make Op codes more easily identified as
to the type, a table of all 1400 system
Op
codes has been made and stored in
local storage.
This table groups simi-
lar Op codes together.
The bit configu-
rations are bit sensitive for easy iden-
tification by the micro program.
(See
Figure 5-6.)
5-7
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