ST92F120 datasheet(90/324 Pages) STMICROELECTRONICS

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ST92F120 - ON-CHIP DIRECT MEMORY ACCESS (DMA)

6.3 DMA TRANSACTIONS

The purpose of an on-chip DMA channel is to

transfer a block of data between a peripheral and

the Register File, or Memory. Each DMA transfer

consists of three operations:

– A load from/to the peripheral data register to/

from a location of Register File (or Memory) ad-

dressed through the DMA Address Register (or

– A post-increment of the DMA Address Register

(or Register pair)

– A post-decrement of the DMA transaction coun-

ter, which contains the number of transactions

that have still to be performed.

If the DMA transaction is carried out between the

peripheral and the Register File (Figure 41), one

one to hold the DMA transaction counter. These

two registers must be located in the Register File:

the DMA Address Register in the even address

next register (odd address). They are pointed to by

the DMA Transaction Counter Pointer Register

(DCPR), located in the peripheral’s paged regis-

ters. In order to select a DMA transaction with the

DCPR) must be set.

If the transaction is made between the peripheral

and Memory, a register pair (16 bits) is required

for the DMA Address and the DMA Transaction

Counter (Figure 42). Thus, two register pairs must

be located in the Register File.

The DMA Transaction Counter is pointed to by the

DMA

Transaction

Counter

Pointer

(DCPR), the DMA Address is pointed to by the

DMA Address

Pointer Register

(DAPR),both

DCPR and DAPR are located in the paged regis-

ters of the peripheral.

Figure 41. DMA Between Register File and Peripheral

IDCR

IVR

DAPR

DCPR

DATA

PAGED

REGISTERS

SYSTEM

DMA

COUNTER

DMA

ADDRESS

FFh

F0h

E0h

DFh

EFh

MEMORY

000000h

DATA

ALREADY

TRANSFERRED

END OF BLOCK

INTERRUPT

SERVICE ROUTINE

DMA

TABLE

ISR ADDRESS

000100h

VECTOR

TABLE

PERIPHERAL

PAGED REGISTERS

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