IBM 5150 Technical Reference page 225

FSTP ; STORE AND POP
ST(O) to IntegerlReal Memory
Escape MF
I
mod 0 1 1 rIm
disp-Iow disp-high
ST(O) to Long Integer Memory
Escape 1 1
I
mod 1
1 rIm
disp-Iow disp-high
ST(O) to Temporary Real Memory
Escape 0 1 1
I
mod 1 1 1 rIm
disp-Iow disp-high
ST(O) to BCD Memory
Escape 1 1 1
I
mod 1 1 0 rIm
disp-Iow disp-high
ST(O) to STm
Escape 1 0
1 1 0 1 1 STO)
FXCH
=
Exchange ST(i) and ST(O)
Escape 0 0 1 1 1 0 0 1 STm
6-18 Instruction Set