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<strong>eZ80</strong> <strong>CPU</strong><br />
User Manual<br />
17<br />
For compare (search) instructions, the Z Flag is set to 1 if a comparison is found<br />
between the value in the Accumulator and the memory located pointed to by the<br />
contents of the register pair HL. When testing a bit in a register or memory<br />
location, the Z Flag contains the complemented state of the indicated bit (see<br />
the BIT b, m instruction).<br />
When inputting or outputting a byte between a memory location and an I/O<br />
device (INI, IND, OUTI and OUTD), if the result of B-1 is zero, the Z Flag is set<br />
to 1. Otherwise, the Z Flag is reset. Also, for byte inputs from I/O devices using<br />
IN r,(C), the Z Flag is set to 1 to indicate a zero byte input.<br />
Sign Flag<br />
The Sign (S) Flag stores the state of the most-significant bit of the Accumulator<br />
(Bit 7). When the <strong>eZ80</strong> performs arithmetic operations on signed numbers,<br />
binary two’s complement notation is used to represent and process numerical<br />
information. A positive number is identified by a 0 in Bit 7. A negative number is<br />
identified by a 1. The binary equivalent of the magnitude of a positive number is<br />
stored in Bits 0-6 for a total range of 0-127. A negative number is represented<br />
by the two’s complement of the equivalent positive number. The total range for<br />
negative numbers is -1 to -128.<br />
When inputting a byte from an I/O device to a register, IN r,(C), the S Flag<br />
indicates either positive (S=0) or negative (S=1) data.<br />
Instructions<br />
The notations in the <strong>eZ80</strong> instructions are defined in the following table.<br />
Table 6. Instruction Notations<br />
Mnemonic<br />
Definition<br />
cc A condition code C, NC, Z, NZ, P, M, PO, PE, V, or NV.<br />
cc’ A condition code C, NC, Z, or NZ.<br />
d An 8-bit signed displacement -128 to 127.<br />
Mmn A 16- or 24-bit immediate value or direct address.<br />
m A, B, C, D, E, H, L, (HL), (IX+d), or (IY+d).<br />
n An 8-bit immediate value or port number in the range of 0-255 or 0-FFH.<br />
p A, B, C, D, E, H, L, n, or (HL)<br />
pp BC, DE, HL, IX+d, or IY+d.<br />
qq BC, DE, HL, SP, IX, or IY.<br />
r, r’ A, B, C, D, E, H, L.<br />
ii IX+d or IY+d.<br />
rr HL, IX, or IY.<br />
s A, B, C, D, E, H, L, n, (HL), (IX+d), or (IY+d).<br />
ss BC, DE, HL, or SP.<br />
tt BC, DE, HL, IX, or IY.<br />
uu HL, IX+d, or IY+d.<br />
vv AF, BC, DE, HL, IX, or IY.<br />
UM007701-1100
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