HD6417615 Hitachi Semiconductor, HD6417615 Datasheet - Page 58

• Manufacturer Part Number: HD6417615
• Description: Hardware Manual
• Manufacturer: Hitachi Semiconductor

2.1.5
DSP unit data operations are fundamentally performed as 32-bit, but these operations are always
executed with a 40-bit length including the 8-bit guard section. When the guard bit section does
not match the value of the 32-bit section MSB, the operation result is treated as an overflow. In
this case, the N bit indicates the correct status of the operation result regardless of the existence or
not of an overflow. This is so even if the destination operand is a 32-bit length register. The 8-bit
section guard bits are always presupposed and each status flag is updated.
When place overflows occur so that the correct result cannot be displayed even when the guard
bits are used, the N flag cannot indicate the correct status.
2.1.6
Table 2.3 lists the values of the registers after reset.
Table 2.3
Classification
General registers
Control registers
System registers
DSP registers
40
Notes on Guard Bits and Overflow Treatment
Initial Values of Registers
Initial Values of Registers
Register
R0–R14
R15 (SP)
SR
RS
RE
GBR
VBR
MOD
MACH, MACL, PR
PC
A0, A0G, A1, A1G, M0,
M1, X0, X1, Y0, Y1
DSR
Initial Value
Undefined
Value of the SP in the vector address table
Bits I3–I0 are 1111 (H'F), the reserved bits, RC, DMY,
and DMX are 0, and other bits are undefined
Undefined
Undefined
H'00000000
Undefined
Undefined
Value of the PC in the vector address table
Undefined
H'00000000