Symbol Description - IBM 5150 Hardware Reference Manual

Register in order to program or obtain the results after a particular
command. The Main Status Register may only be read and is used to
facilitate the transfer of data between the processor and FDC.
The bits in the Main Status Register are defmed as follows:
Bit
Number
Name
Symbol Description
DBOFDD
FDDABusy DAB
FDD number is in the
Seek mode.
DBI FDD B Busy
DBB
FDD number I is in the
Seek mode.
DB2 FDD C Busy DCB FDD number 2 is in the
Seek mode.
DB3 FDDDBusy
DDB
FDD number 3 is in the
Seek mode.
DB4 FDC Busy
CB
A read or write command
is in process.
DB5
Non-DMA
NDM
The FDC is in the non-
Mode DMAmode.
DB6 Data Input! DIO Indicates direction of data
transfer between FDC
and Processor. If
D I 0
=
"I", then transfer
is from FDC Data Regis ­
-
ter to the Processor, If
DIO
=
"0", then transfer
is from the Processor to
FDC Data Register.
DB7 Request for
RQM
Indicates Data Register is
Master ready to send or receive
data to or from the Pro­
cessor. Both bits DIO and
RQM should be used to
perform the handshaking
functions of "ready" and
"direction" to the
processor.
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