ST92T163 ST Microelectronics, ST92T163 Datasheet - Page 72

• Manufacturer Part Number: ST92T163
• Description: 8/16-BIT FULL SPEED USB MCU FOR COMPOSITE DEVICES WITH 16 ENDPOINTS
• Manufacturer: ST Microelectronics

ST92163 - ON-CHIP DIRECT MEMORY ACCESS (DMA)
DMA TRANSACTIONS (Cont’d)
When selecting the DMA transaction with memory,
bit DCPR.RM (bit 0 of DCPR) must be cleared.
To select between using the ISR or the DMASR reg-
ister to extend the address, (see Memory Manage-
ment Unit chapter), the control bit DAPR.PS (bit 0
of DAPR) must be cleared or set respectively.
The DMA transaction Counter must be initialized
with the number of transactions to perform and will
be decremented after each transaction. The DMA
Address must be initialized with the starting ad-
dress of the DMA table and is increased after each
transaction. These two registers must be located
between addresses 00h and DFh of the Register
File.
Once a DMA channel is initialized, a transfer can
start. The direction of the transfer is automatically
defined by the type of peripheral and programming
mode.
Once the DMA table is completed (the transaction
counter reaches 0 value), an Interrupt request to
the CPU is generated.
Figure 33. DMA Between Memory and Peripheral
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PAGED REGISTERS
PERIPHERAL
DAPR
DCPR
DATA
IDCR
IVR
FFh
F0h
EFh
E0h
DFh
REGISTER FILE
TRANSACTION
REGISTERS
REGISTERS
COUNTER
ADDRESS
SYSTEM
PAGED
DMA TRANSACTION
DMA
DMA
When the Interrupt Pending (IP) bit is set by a
hardware event (or by software), and the DMA
Mask bit (DM) is set, a DMA request is generated.
If the Priority Level of the DMA source is higher
than, or equal to, the Current Priority Level (CPL),
the DMA transfer is executed at the end of the cur-
rent instruction. DMA transfers read/write data
from/to the location pointed to by the DMA Ad-
dress Register, the DMA Address register is incre-
mented and the Transaction Counter Register is
decremented. When the contents of the Transac-
tion Counter are decremented to zero, the DMA
Mask bit (DM) is cleared and an interrupt request
is generated, according to the Interrupt Mask bit
(End of Block interrupt). This End-of-Block inter-
rupt request is taken into account, depending on
the PRL value.
WARNING. DMA requests are not acknowledged
if the top level interrupt service is in progress.
0000h
0100h
SERVICE ROUTINE
TRANSFERRED
END OF BLOCK
ISR ADDRESS
INTERRUPT
ALREADY
MEMORY
DATA
VECTOR
TABLE
TABLE
DMA