IBM System/360 Field Engineering Manual page 29

"'
0
Operation
Zero and Add
Mnemonic
ZAP
Op Code Format Operands
FS SS Dl(Ll,Bl),
D2(L2,B2)
Description InterruptiE~ _g~~
Opr 1 cleared and opr 2 placed in opr 1 Prat O Result= O
(Low-order opr 's may coincide) Adr 1 Result < 0
(Opr 2 must be in packed format) Data 2 Result > O
(Opr 1 field must be large enough for all Dec Oflo 3
Overflow
opr
2
significant digits)