S1C17 CORE MANUAL
Seiko Epson Corporation
3-1
(Rev. 1.2)
3 Data Formats
3.1 Data Formats Handled in Operations Between Registers
The S1C17 Core can handle 8-, 16-, and 24-bit data in register operations. In this manual, data sizes are expressed
as follows:
8-bit data
Byte
,
B
, or
b
16-bit data
Word
,
W
, or
w
24-bit data
Address data
,
A
,
a
Data sizes can be selected only in data transfer (load instruction) between one general-purpose register and another.
In an 8-bit data transfer with a general-purpose register as the destination, the data is sign- or zero-extended to 16
bits before being loaded into the register. Whether the data will be sign- or zero-extended is determined by the load
instruction used.
In a 16-bit or 8-bit data transfer using a general-purpose register as the source, the data to be transferred is stored in
the low-order 16 bits or the low-order 8 bits of the source register.
The data transfer sizes and types are described below.
3.1.1 Unsigned 8-Bit Transfer (Register
→
Register)
Example:
ld.ub %rd,%rs
%rs
X
23
16
X
15
8
Byte
7
0
23
16 15
8
Byte
7
0
0
%rd
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 3.1.1.1 Unsigned 8-Bit Transfer (Register
→
Register)
Bits 23–8 in the destination register are set to 0x0000.
3.1.2 Signed 8-Bit Transfer (Register
→
Register)
Example:
ld.b %rd,%rs
%rs
X
23
16
X
15
8 7
0
23
16 15
8
Byte
7
0
%rd
S
S
S
S
S
S
S
S
S
S
Byte
0
0
0
0
0
0
0
0
0
Figure 3.1.2.1 Signed 8-Bit Transfer (Register
→
Register)
Bits 15–8 in the destination register are sign-extended and bits 23–16 are set to 0x00.
