Name _________________________
CpE 310 Microprocessor Systems
Quiz #6
80x86
1. How many 8-bit general purpose registers are available in the 8086/8088? What are their
names?
8: AH, AL, BH, BL, CH, CL, and DH, DL
2. How many 16-bit general purpose registers are available in the 8086/8088? What are
their names? Why is the CX register called the count register? Why is the DX register
called the data register? List the five pointer and index registers and explain their normal
function.
4: AX, BX, CX, and DX
CX reserves as a count register for Loop, REP, and Shift/Rotate instructions
DX can be used to store data from certain instruction, eg. MUL, DIV, …..
[BX], [SI], [DI], [SP], [IP]
3. Segment registers are used to address a 64K-byte block of memory. How is this possible
when a segment register is only 16 bits wide and the memory address is 20 bits wide? Can
memory segments overlap? If so, what is the minimum number of overlapped bytes other
than 0?
Offset the segment register by shift 4 bits to the left then add to EA to form 20 bit physical
address.
Yes, it can overlap.
Minimum overlap other than 0 is 16 bytes (4 bits)
Klinkhachorn:Cpe 310:2/13/04