dsp56800 Freescale Semiconductor, Inc, dsp56800 Datasheet - Page 83

• Manufacturer Part Number: dsp56800
• Description: 16-bit Digital Signal Controllers
• Manufacturer: Freescale Semiconductor, Inc

All four address pointer registers and the SP are used in generating addresses in the register indirect
addressing modes. The offset register can be used by all four address pointer registers and the SP, whereas
the modulo register can be used by the R0 or by both the R0 and R1 pointer registers.
Whereas all the address pointer registers and the SP can be used in many addressing modes, there are some
instructions that only work with a specific address pointer register. These cases are presented in Table 4-5
on page 4-9.
The address generation unit is connected to four major buses: CGDB, XAB1, XAB2, and PAB. The
CGDB is used to read or write any of the address generation unit registers. The XAB1 and XAB2 provide
a primary and secondary address, respectively, to the X data memory, and the PAB provides the address
when accessing the program memory.
A block diagram of the address generation unit is shown in Figure 4-1, and its corresponding programming
model is shown in Figure 4-2. The blocks and registers are explained in the following subsections.
Freescale Semiconductor
M01
15
Pointer
Registers
R0
R1
R2
R3
SP
Figure 4-2. Address Generation Unit Programming Model
Figure 4-1. Address Generation Unit Block Diagram
N
0
CGDB(15:0)
Address Generation Unit
15
Arithmetic
Modulo
Unit
PAB(15:0)
Register
Offset
N
0
XAB1(15:0)
Architecture and Programming Model
SP
R0
R1
R2
R3
15
R3 Only
XAB2(15:0)
Register
Modifier
M01
Inc./Dec.
0
AA0014
AA0015
4-3