Samsung KS57C2308 Manual page 18

ADDRESS SPACES
Special-Purpose Working Registers
Register A is used as a 4-bit accumulator and double register EA as an 8-bit accumulator. The carry flag can also
be used as a 1-bit accumulator.
8-bit double registers WX, WL and HL are used as data pointers for indirect addressing. When the HL register
serves as a data pointer, the instructions LDI, LDD, XCHI, and XCHD can make very efficient use of working
registers as program loop counters by letting you transfer a value to the L register and increment or decrement it
using a single instruction.
Recommendation for Multiple Interrupt Processing
If more than four interrupts are being processed at one time, you can avoid possible loss of working register data
by using the PUSH RR instruction to save register contents to the stack before the service routines are executed
in the same register bank. When the routines have executed successfully, you can restore the register contents
from the stack to working memory using the POP instruction.
2-10
EA
Figure 2-6. 1-Bit, 4-Bit, and 8-Bit Accumulator
1-BIT
C
ACCUMULATOR
4-BIT
A
ACCUMULATOR
8-BIT
ACCUMULATOR
KS57C2308/P2308/C2316/P2316