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ST72P63BE1M1 Datasheet(PDF) 84 Page - STMicroelectronics

Part No. ST72P63BE1M1
Description  Low speed USB 8-bit MCU family with up to 32K Flash/ROM, DFU capability, 8-bit ADC, WDG, timer, SCI & I²C
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com
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ST72P63BE1M1 Datasheet(HTML) 84 Page - STMicroelectronics

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USB interface (Cont’d)
12.4.5 Programming considerations
The interaction between the USB interface and the
application program is described below. Apart
from system reset, action is always initiated by the
USB interface, driven by one of the USB events
associated with the Interrupt Status Register (IS-
TR) bits.
12.4.5.1 Initializing the registers
At system reset, the software must initialize all reg-
isters to enable the USB interface to properly gen-
erate interrupts and DMA requests.
1. Initialize the DMAR, IDR, and IMR registers
(choice of enabled interrupts, address of DMA
buffers). Refer the paragraph titled initializing
the DMA Buffers.
2. Initialize the EP0RA and EP0RB registers to
enable accesses to address 0 and endpoint 0
to support USB enumeration. Refer to the para-
graph titled Endpoint Initialization.
3. When addresses are received through this
channel, update the content of the DADDR.
4. If needed, write the endpoint numbers in the EA
fields in the EP1RB and EP2RB register.
12.4.5.2 Initializing DMA buffers
The DMA buffers are a contiguous zone of memo-
ry whose maximum size is 48 bytes. They can be
placed anywhere in the memory space to enable
the reception of messages. The 10 most signifi-
cant bits of the start of this memory area are spec-
ified by bits DA15-DA6 in registers DMAR and
IDR, the remaining bits are 0. The memory map is
shown in Figure 42.
Each buffer is filled starting from the bottom (last 3
address bits=000) up.
12.4.5.3 Endpoint initialization
To be ready to receive:
Set STAT_RX to VALID (11b) in EP0RB to enable
reception.
To be ready to transmit:
1. Write the data in the DMA transmit buffer.
2. In register EPnRA, specify the number of bytes
to be transmitted in the TBC field
3. Enable the endpoint by setting the STAT_TX
bits to VALID (11b) in EPnRA.
Note: Once transmission and/or reception are en-
abled, registers EPnRA and/or EPnRB (respec-
tively) must not be modified by software, as the
hardware can change their value on the fly.
When the operation is completed, they can be ac-
cessed again to enable a new operation.
12.4.5.4 Interrupt handling
Start of Frame (SOF)
The interrupt service routine may monitor the SOF
events for a 1 ms synchronization event to the
USB bus. This interrupt is generated at the end of
a resume sequence and can also be used to de-
tect this event.
USB Reset (RESET)
When this event occurs, the DADDR register is re-
set, and communication is disabled in all endpoint
registers (the USB interface will not respond to any
packet). Software is responsible for reenabling
endpoint 0 within 10 ms of the end of reset. To do
this, set the STAT_RX bits in the EP0RB register
to VALID.
Suspend (SUSP)
The CPU is warned about the lack of bus activity
for more than 3 ms, which is a suspend request.
The software should set the USB interface to sus-
pend mode and execute an ST7 HALT instruction
to meet the USB-specified power constraints.
End Suspend (ESUSP)
The CPU is alerted by activity on the USB, which
causes an ESUSP interrupt. The ST7 automatical-
ly terminates Halt mode.
Correct Transfer (CTR)
1. When this event occurs, the hardware automat-
ically sets the STAT_TX or STAT_RX to NAK.
Note: Every valid endpoint is NAKed until soft-
ware clears the CTR bit in the ISTR register,
independently
of
the
endpoint
number
addressed by the transfer which generated the
CTR interrupt.
Note: If the event triggering the CTR interrupt is
a SETUP transaction, both STAT_TX and
STAT_RX are set to NAK.
2. Read the PIDR to obtain the token and the IDR
to get the endpoint number related to the last
transfer.
Note: When a CTR interrupt occurs, the TP3-
TP2 bits in the PIDR register and EP1-EP0 bits
in the IDR register stay unchanged until the
CTR bit in the ISTR register is cleared.
3. Clear the CTR bit in the ISTR register.


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