8051 Microcontroller, Internals, Instructions, Programming and Interfacing, 2nd Edition

32

I/O PORTS AND SPECIAL FUNCTION REGISTERS

ACC.7

E7 E6 E5 E4 E3 E2 E1 E0

ACC.6 ACC.5 ACC.4 ACC.3 ACC.2 ACC.1 ACC.0

(LSB)(MSB)

ACCUMULATOR

(reg. A)

Direct Address E0H

Individual bit address

Figure 3.4 Details of the accumulator (SFR) of MCS-51

Fig. 3.3 explains the conditions of setting of carry (CY), auxiliary carry (AC) and overfl ow (OV) fl ags of the

PSW SFR.

76543

Data out from

bit 7

Data out from

bit 3 to bit 4

Data out from bit

6 to bit 7 but not

from bit 7

Data out from

bit 7 but not

from bit 6 to

bit 7

X

X

AC OV

or

CY

210 76543210 76543210 76543210

Figure 3.3 Conditions for setting of CY, AC and OV fl ags of PSW SFR

A simpler method to remember relative locations ...