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ADSP-21MOD870

Internet Gateway Processor

Analog Devices 

ADSP-21mod870

held at a constant level and will not oscillate if the three-state

driver’s level hovers around the logic switching point.

MEMORY ARCHITECTURE

The ADSP-21mod870 provides a variety of memory and pe-

ripheral interface options. The key functional groups are Pro-

gram Memory, Data Memory, Byte Memory and I/O. Refer to

the following figures and tables for PM and DM memory alloca-

tions in the ADSP-21mod870.

Program Memory

The Program Memory map is shown in Figure 5.

Program Memory (Full Memory Mode) is a 24-bit space for

storing both instruction op codes and data. The ADSP-21mod870

has 32K words of Program Memory RAM on chip, and the

capability of accessing up to two 8K external memory overlay

spaces using the external data bus.

Program Memory (Host Mode) allows access to all internal

memory. External overlay access is limited by a single external

address line (A0). External program execution is not available in

host mode due to a restricted data bus that is 16 bits wide only.

The PMOVLAY bits are defined in Table III.

Table III. PMOVLAY Bits

PMOVLAY

0, 4, 5

1

2

Memory A13

Internal Not Applicable

External 0

Overlay 1

External 1

Overlay 2 1

A12:0

Not Applicable

13 LSBs of Address

Between 0x2000

and 0x3FFF

13 LSBs of Address

Between 0x2000

and 0x3FFF

Data Memory

The Data Memory map is shown in Figure 6.

PM MODE B=0

PM (MODE B=1)1

ALWAYS

ACCESSIBLE

RESERVED

AT ADDRESS

0x0000 – 0x1FFF

0x2000–

0x3FFF

ACCESSIBLE WHEN

PMOVLAY = 0

0x2000–

0x3FFF

0x2000–

0x3FFF

ACCESSIBLE WHEN

PMOVLAY = 0

INTERNAL

MEMORY

RESERVED

INTERNAL ACCESSIBLE WHEN

MEMORY PMOVLAY = 4

0x2000–

0x3FFF

RESERVED

0x0000–

0x1FFF2

ACCESSIBLE WHEN

PMOVLAY = 5

ACCESSIBLE WHEN

PMOVLAY = 1

0x2000–

0x3FFF2

0x2000–

0x3FFF2

ACCESSIBLE WHEN

PMOVLAY = 1

EXTERNAL

MEMORY

RESERVED

EXTERNAL

MEMORY

ACCESSIBLE WHEN

PMOVLAY = 2

1WHEN MODE = 1, PMOVLAY MUST BE SET TO 0

2SEE TABLE III FOR PMOVLAY BITS

PROGRAM MEMORY

MODE B = 0 ADDRESS

0x3FFF

8K INTERNAL

PMOVLAY = 0, 4, 5

OR

8K EXTERNAL

PMOVLAY = 1, 2

0x2000

0x1FFF

8K INTERNAL

PROGRAM MEMORY

MODE B = 1 ADDRESS

0x3FFF

8K INTERNAL

PMOVLAY = 0

8K EXTERNAL

0x2000

0x1FFF

0x0000

Figure 5. Program Memory

0x0000

DATA MEMORY

ALWAYS

ACCESSIBLE

AT ADDRESS

0x2000 – 0x3FFF

0x2000–

ACCESSIBLE WHEN 0x1FFF

DMOVLAY = 0

0x0000–

0x1FFF

INTERNAL

MEMORY

ACCESSIBLE WHEN

DMOVLAY = 4

ACCESSIBLE WHEN

DMOVLAY = 5

0x0000–

0x1FFF

0x0000–

0x1FFF

ACCESSIBLE WHEN

DMOVLAY = 1

EXTERNAL

MEMORY

ACCESSIBLE WHEN

DMOVLAY = 2

0x0000–

0x1FFF

DATA MEMORY

32 MEMORY

MAPPED

REGISTERS

INTERNAL

8160

WORDS

ADDRESS

0x3FFF

0x3FE0

0x3FDF

0x2000

0x1FFF

8K INTERNAL

DMOVLAY = 0, 4, 5

OR

EXTERNAL 8K

DMOVLAY = 1, 2

0x0000

Figure 6. Data Memory Map

REV. 0

–9–

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