The X86 Microprocessors: Architecture and Programming (8086 to Pentium), 1st Edition

296 THE x86 MICROPROCESSORS

Bit Assignment of the Control Word First look at D7 – it suggests the options of I/O mode

or BSR mode. To begin with, let us use the chip in the I/O mode.  is is the normal mode of

operation (BSR mode is a special mode catering to Port C alone which we will deal with, later).

 e next thing to do in this, is to decide the mode of operation of the two groups. It is accep

table

for the two groups to be in diff erent or same modes. After this is done, select the option of a

particular port being either an input or output port. For i/p, the corresponding bit is to be 1, and

for output it is to be 0.

9.3 | Modes of Opera ...