Editing IBM 1401 (section)

===Modifiers for five-character Branch on Indicator (B) instruction===
The B opcode, if followed by a three-character operand, was a simple unconditional branch to the indicated address. If a fourth operand character was  present (making five characters total including the opcode), this made it a conditional branch. This "modifier" character specified the condition to be tested.

{| class="wikitable"
|-
! [[Binary-coded decimal#IBM and BCD|BCD]] Character
! Unit
! Meaning
|-
| align="center" | Blank
| 1401
| Unconditional—no word mark needed in next character
|-
| align="center" | 1
| 1009
| in run condition
|-
| &nbsp;
| 1011
| punch in backspace operation
|-
| &nbsp;
| 1011
| reader parity indicator on
|-
| &nbsp;
| 1231
| auto select
|-
| &nbsp;
| 1285
| error
|-
| &nbsp;
| 1412
| control-check indicator on
|-
| &nbsp;
| 1418
| late read
|-
| &nbsp;
| 1419
| document to be read
|-
| &nbsp;
| 1428
| late read or late reading mode change
|-
| &nbsp;
| 1445
| printer error
|-
| &nbsp;
| 7340
| hypertape unusual end
|-
| &nbsp;
| 7740
| transmission complete with abnormal status
|-
| &nbsp;
| DDC
| transmission error
|-
| align="center" | 2
| 1009
| buffer available
|-
| &nbsp;
| 1011
| punch ready
|-
| &nbsp;
| 1011
| reader ready
|-
| &nbsp;
| 1231
| full buffer
|-
| &nbsp;
| 1285
| end of line
|-
| &nbsp;
| 1412
| reader-not-ready signal on
|-
| &nbsp;
| 1418
| ready to engage
|-
| &nbsp;
| 1419
| document under read head (PDS 4)
|-
| &nbsp;
| 1428
| ready to engage
|-
| &nbsp;
| 7340
| hypertape normal end
|-
| &nbsp;
| 7740
| transmission complete successfully
|-
| &nbsp;
| DDC
| transmission ended by GMWM
|-
| align="center" | 3
| 1009
| good transmission occurred
|-
| &nbsp;
| 1011
| punch not ready to receive data
|-
| &nbsp;
| 1231
| ready to read
|-
| &nbsp;
| 1285
| reader transporting
|-
| &nbsp;
| 1412
| read-check indicator on
|-
| &nbsp;
| 1418
| document under selected read station
|-
| &nbsp;
| 1419
| valid amount field
|-
| &nbsp;
| 1428
| document under selected read station
|-
| &nbsp;
| 7340
| hypertape control unit 7641 busy
|-
| &nbsp;
| 7740
| receive request
|-
| &nbsp;
| DDC
| read request
|-
| align="center" | 4
| 1009
| reply-bad indicator on
|-
| &nbsp;
| 1011
| punch not ready to read
|-
| &nbsp;
| 1231
| empty hopper
|-
| &nbsp;
| 1285
| marked line
|-
| &nbsp;
| 1412
| amount-field indicator on
|-
| &nbsp;
| 1419
| valid process-control field
|-
| &nbsp;
| 7340
| hypertape attention
|-
| &nbsp;
| 7740
| 7740 attention
|-
| &nbsp;
| DDC
| write request
|-
| align="center" | 5
| 1009
| error reply acknowledgement
|-
| &nbsp;
| 1011
| punch overextended
|-
| &nbsp;
| 1231
| read error or overrun
|-
| &nbsp;
| 1285
| header information
|-
| &nbsp;
| 1412
| process-control indicator on
|-
| &nbsp;
| 1418
| document end
|-
| &nbsp;
| 1419
| valid account-number field
|-
| &nbsp;
| 1428
| document end
|-
| &nbsp;
| 1445
| printer busy
|-
| align="center" | 6
| 1009
| program attention required
|-
| &nbsp;
| 1011
| punch supply reel low or chad box full
|-
| &nbsp;
| 1231
| timing mark check
|-
| &nbsp;
| 1285
| ready to read a line
|-
| &nbsp;
| 1412
| account-number indicator on
|-
| &nbsp;
| 1418
| character on line
|-
| &nbsp;
| 1419
| valid transit-number field
|-
| &nbsp;
| 1428
| character on line
|-
| &nbsp;
| 1445
| carriage busy
|-
| &nbsp;
| DDC
| write in progress
|-
| align="center" | 7
| 1009
| end of message
|-
| &nbsp;
| 1285
| reader ready
|-
| &nbsp;
| 1412
| transit-number indicator on
|-
| &nbsp;
| 1418
| empty hopper and transport (end of file)
|-
| &nbsp;
| 1419
| valid serial-number field
|-
| &nbsp;
| 1428
| empty hopper and transport (end of file)
|-
| &nbsp;
| 1445
| carriage channel 9
|-
| &nbsp;
| DDC
| read in progress
|-
| align="center" | 8
| 1009
| end of file
|-
| &nbsp;
| 1285
| end of file
|-
| &nbsp;
| 1412
| document-spacing-check indicator on
|-
| &nbsp;
| 1418
| ready to read
|-
| &nbsp;
| 1419
| auto-select
|-
| &nbsp;
| 1428
| ready to read
|-
| &nbsp;
| 1448
| carriage channel 12
|-
| &nbsp;
| DDC
| system A stopped
|-
| align="center" | 9
| 1403
| carriage tape channel 9
|-
| align="center" | 0
| 1404
| validity error
|-
| align="center" | ' or @
| 1403
| carriage tape channel 12
|-
| align="center" | >
| 1448
| end of block
|-
| align="center" | /
| 1401
| unequal compare
|-
| align="center" | S
| 1401
| equal compare
|-
| align="center" | T
| 1401
| low compare
|-
| align="center" | U
| 1401
| high compare
|-
| align="center" | V
| 1301
| disk error
|-
| &nbsp;
| 1311
| disk error
|-
| &nbsp;
| 1405
| read or write parity check or read back check error
|-
| align="center" | W
| 1301
| wrong-length record
|-
| &nbsp;
| 1311
| wrong-length record
|-
| &nbsp;
| 1405
| wrong-length record
|-
| align="center" | X
| 1301
| unequal address compare
|-
| &nbsp;
| 1311
| unequal address compare
|-
| &nbsp;
| 1405
| unequal address compare
|-
| align="center" | Y
| 1301
| any disk-unit error condition
|-
| &nbsp;
| 1311
| any disk-unit error condition
|-
| &nbsp;
| 1405
| any disk-unit error condition
|-
| align="center" | Z
| 1401
| arithmetic overflow
|-
| align="center" | ‡
| 1403
| printer error (record mark)
|-
| align="center" | ( or %
| 1401
| process check with process check switch off
|-
| &nbsp;
| 1440
| I/O check stop switch off
|-
| align="center" | \
| 1301
| access busy
|-
| &nbsp;
| 1311
| access busy
|-
| align="center" | J
| 1419
| I/O channel-busy indicator
|-
| &nbsp;
| TAU
| tape busy
|-
| &nbsp;
| SIO
| serial input-output busy
|-
| align="center" | K
| TAU
| end of reel (writing) or tape mark (reading)
|-
| align="center" | L
| TAU
| tape error
|-
| align="center" | N
| 1301
| access inoperable
|-
| &nbsp;
| 1311
| access inoperable
|-
| &nbsp;
| 1405
| access inoperable
|-
| align="center" | P
| 1403
| printer busy
|-
| align="center" | Q
| 1407
| inquiry request
|-
| align="center" | R
| 1403
| carriage busy
|-
| align="center" | !
| 1402
| punch error
|-
| align="center" | *
| 1407
| inquiry clear
|-
| align="center" | + or &
| 1442
| last card (Reader unit 2)
|-
| align="center" | A
| 1402
| last card if SS A is on
|-
| align="center" | B
| 1401
| SS B
|-
| &nbsp;
| 7340
| hypertape attention response
|-
| align="center" | C
| 1401
| SS C
|-
| align="center" | D
| 1401
| SS D
|-
| align="center" | E
| 1401
| SS E
|-
| &nbsp;
| 7340
| hypertape end response
|-
| align="center" | F
| 1401
| SS F
|-
| align="center" | G
| 1401
| SS G
|-
| align="center" | H
| 1402
| reader busy
|-
| align="center" | I
| 1402
| punch busy
|-
| align="center" | ?
| 1402
| reader error
|-
| align="center" | <
| 1448
| early warning
|-
|}

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