IBM 5150 Hardware Reference Manual page 114

Table 13.
Symbol Descriptions (continued)
SYMBOL NAME
NO Non-DMA Mode
PCN Present Cylinder
Number
R Record
R/W Read/Write
SC Sector
SK Skip
SRT Step Rate Time
ST 0 Status 0
ST 1 Status 1
ST 2 Status 2
ST3 Status 3
STP Scan Test
USO, Unit Select
US1
DESCRIPTION
ND stands for operation in the Non-DMA Mode.
PCN stands for Cylinder number at the comple­
tion of SENSE INTER RUPT STATUS Command,
indicating the position of the Head at present
time.
Rstands for the Sector number, which will
be read or written.
R!W stands for either Read (R) or Write (W)
signal.
SC indicates the number of Sectors per Cylinder.
SK stands for Skip Deleted Data Address Mark.
SRT stands for the Stepping Rate for the FDD.
(2 to 32 ms in 2 ms increments'!
ST 0-3 stand for one of four registers which
store the status information after a command
has been executed. This information is available
during the result phase after command execu­
tion. These registers should not be confused
with the main status register (selected by AO
=
0).
ST 0-3 may be read only after a command has
been executed and contain information
relevant to that particular command.
During a Scan operation, if STP
=
1, the data in
contiguous sectors is compared byte by byte
with data sent from the processor (or DMA),
and if STP
=
2, then alternate sectors are
read and compared.
US stands for a selected drive number
encoded the same as bits 0 and 1
of the digital register (DOR) p 2-91
2-95