8085

My question is why are there 6T states in opcode fetch of the CALL instruction while there are 4 for other instructions in 8085 microprocessor. I have searched a lot but didn't find any satisfactory answer. Here: http://www.edaboard.com/thread201650.html it says that it has something to do with dual addressing modes being used in case of CALL. But doesn't really explain why 6T states. Any idea? EDIT This question arose when I came to know that CALL takes 18 T-states. According to my calculations it should be: 4(for opcode fetch) + 3 + 3 (two memory reads to read the subroutine address) + 3 + 3

In the flag register of Z80, 8080, 8085, and 8086 processors, what is the purpose of bits 1, 3, 5, which are documented as "reserved" or "undefined"? Konamiman These bits are unused; that is, no instruction explicitly sets them to any value. The designers decided that 5/6 flags was enough, and they just left the remaining bits of the flags register unused. They are documented as being "undefined" because it is not possible to know in advance which value will they have after any of the instructions are executed—the processor design is simpler that way, as opposed to setting them explicitly to 0

It is said that the subtraction is performed in 2's complement in 8085 and so the flags must be set according to the operation. However,in the figure shown, i am unable to figure out the reason behind auxiliary carry flag being set to '0' and the same goes for carry flag. When i performed 2's complement operation, i found carry=1 (which is not taken into consideration in 2's complement) and i also found carry of 1 shifting from lower nibble to upper and so i thought auxiliary carry to be 1. But i found just the opposite for both of them. Similarly in the second case shown below, manually i got

When studying programming 8085, 8086 and microporcessors in general we always have hexadecimal representation. Its ok that binary numbers are important in computers. But how these hexadecimal numbers are important? Any historical importance? It would be nice if someone point to some historical papers also. EDIT: How computers handle hexadecimal numbers? For example what happens in 8085 when a hexadecimal number is given as input? Hexadecimal has a closer visual mapping to the various bytes used to store a number than decimal does. For example, you can tell from the hexadecimal number