Question

The Game Boy Z80 CPU has a half-carry flag, and I can t seem to find much information about when to set/clear it.

我迄今理解的是,任何8个轨道增加、分立、转移或轮换作业(可能还有其他)都将其设定为成果第4项的范围,而DAA指令则将这一节奏/使用。我不肯定的是,16项指示是如何影响到它的,它是否受到某些登记册的使用的影响。

Answer 1

它从第3轨到第4轨,就像正常的国旗记录从第7轨起一样。因此,例如,在增加数中增加一半:

((a&0xf) + (value&0xf))&0x10

Which gives 0x10 if half carry should be set, 0 otherwise. Getting half carry from the other relevant ops follows naturally - the questions is whether there was carry from the low nibble to the high.

为了把事情看上去,z80有四比一的“ALU”,并且用两条四点眼镜进行8倍。因此,由于中间结果,它自然会占一半。

DAA is interested in the flag because if half carry is set then two digits that add up to more than 16 were added in the low nibble; that will have correctly produced carry into the upper nibble but will have left the low nibble 6 lower than it should be, since there were six more values between 10, when it should have generated carry, and 16, when it did.

Answer 2

在16个轨道操作中,在高度按吨位的登记册中,从第3轨到第4轨。换言之,轨道11至轨道12。

(Note the above bits are labeled 0-15, from least to most significant)

See here: http://www.z80.info/z80code.htm

16 bit arithmetic

If  you want to add numbers that are more than the 0-255 that can
be stored in the A register,  then the HL, IX or IY registers can
be used. Thus LD HL,1000H:LD BC,2000H:ADD HL,BC will give

A  CZPSNH  BC   DE   HL   IX   IY  A  CZPSNH  BC   DE   HL   SP
00 000000 2000 0000 3000 0000 0000 00 000000 0000 0000 0000 0000

The flags are set as follows.

C or carry flag          1 if answer >65535 else 0
Z or zero flag           not changed
P flag                   not changed
S or sign flag           not changed
N flag                   0
H or half carry flag     1 if carry from bit 11 to bit 12 else 0

Answer 3

由于半边疆旗是博爱艺术家最常见的 blocks脚石之一,我冒着自由把与最近一个地雷问题联系起来作为答案:

Game:半衰期旗和16轨指示(特别是代码0xE8)

A summary of the above thread (answer by @gekkio):

It depends on the instruction, but the flags are always updated based on the same bit positions if you think in terms of 8-bit values...it just varies whether we re talking about the high or low byte of the 16-bit value. Bit 11 is just bit 3 of the high byte.

ADD SP, e: H from bit 3, C from bit 7 (flags from low byte op)

LD HL, SP+e: H from bit 3, C from bit 7 (flags from low byte op)

ADD HL, rr: H from bit 11, C from bit 15 (flags from high byte op)

INC rr: no flag updates (executed by the 16-bit inc/dec unit)

DEC rr: no flag updates (executed by the 16-bit inc/dec unit)

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