Nintendo Ultra64 Programmer's Manual page 205

SB
31 26 25
SB
1 0 1 0 0 0
6
Format:
sb rt, offset(base)
Description:
offset
The 16-bit
DMEM address. The least-significant byte of register
Since DMEM is only 4K bytes, only the lower 12 bits of the effective address are used.
Operation:

T:
Addr ((offset
data  GPR
StoreDMEM (BYTE, data, Addr
Exceptions:
None
Revision 1.0
Store Byte
21 20 16
base rt
5 5
is sign-extended and added to the contents of general register
16
) || offset
15 15...0
7...0
15
offset
16
rt
is stored at the DMEM address.
) + GPR[base]
)
11...0
SB
0
base
to form a
205