
Address Generation Unit
SC140 DSP Core Reference Manual 2-37
2.3.2.6 Modifier Control Register (MCTL)
The MCTL register is a 32-bit read/write register. This control register is used to program the address
mode (AM) for each of the eight low address registers (R0–R7). The addressing mode of the high address
register file (R8–R15) cannot be programmed and functions in linear addressing mode only. The format of
MCTL is shown in Figure 2-14.
Figure 2-14. Modifier Control Register (MCTL) Format
The AM bits (AM3, AM2, AM1, AM0) associated with each address register (R0-R7) reflect the address
modifier mode of this address register as shown in Table 2-17. Each of the Rn registers can use M0, M1,
M2, or M3 as their associated modulo register either in modulo addressing mode, or in multiple
wrap-around modulo addressing mode. When activating the modulo addressing mode, the corresponding
B register is used to define the lower boundary value (B0 with R0, and so on). The linear or the
reverse-carry addressing modes can also be used, freeing the B register to be used as an additional linear
address register.
The high bank of the address register file (R8–R15) can only be used in linear addressing mode. Each Rn
(n = 8:15) is available only if the corresponding B
n
-8
register is not used since both Rn and B
n
-8
are mapped
to the same physical register.
MCTL is initialized to zero at reset, setting a default linear mode for all Rn registers. All other AM field
combinations are reserved and should not be used.
Bit 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 Bit 16
R7 AM[3:0] R6 AM[3:0] R5 AM[3:0] R4 AM[3:0]
Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Bit 0
R3 AM[3:0] R2 AM[3:0] R1 AM[3:0] R0 AM[3:0]
Table 2-17. Address Modifier (AM) Bits
AM3 AM2 AM1 AM0 Address Modifier Modes
0000 Linear addressing
0001 Reverse-carry addressing
1000 M0 used—Modulo addressing
1001 M1 used—Modulo addressing
1010 M2 used—Modulo addressing
1011 M3 used—Modulo addressing
1100 M0 used—Multiple wrap-around modulo addressing
1101 M1 used—Multiple wrap-around modulo addressing
1110 M2 used—Multiple wrap-around modulo addressing
1111 M3 used—Multiple wrap-around modulo addressing
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