at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 281

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Receiver Time-out
1790A–ATARM–11/03
The Receiver Time-out provides support in handling variable-length frames. This feature
detects an idle condition on the RXD line. When a time-out is detected, the bit TIMEOUT in the
Channel Status Register (US_CSR) rises and can generate an interrupt, thus indicating to the
driver an end of frame.
The time-out delay period (during which the receiver waits for a new character) is programmed
in the TO field of the Receiver Time-out Register (US_RTOR). If the TO field is programmed at
0, the Receiver Time-out is disabled and no time-out is detected. The TIMEOUT bit in
US_CSR remains at 0. Otherwise, the receiver loads a 16-bit counter with the value pro-
grammed in TO. This counter is decremented at each bit period and reloaded each time a new
character is received. If the counter reaches 0, the TIMEOUT bit in the Status Register rises.
The user can either:
•
•
If STTTO is performed, the counter clock is stopped until a first character is received. The idle
state on RXD before the start of the frame does not provide a time out. This prevents having to
obtain a periodic interrupt and enables a wait of the end of frame when the idle state on RXD
is detected.
If RETTO is performed, the counter starts counting down immediately from the value TO. This
enables generation of a periodic interrupt so that a user time-out can be handled, for example
when no key is pressed on a keyboard.
Figure 102 shows the block diagram of the Receiver Time out feature.
Figure 102. Receiver Time-out Block Diagram
Table 50 gives the maximum time-out period for some standard baud rates.
RETTO
Obtain an interrupt when a time-out is detected after having received at least one
character. This is performed by writing the Control Register (US_CR) with the STTTO
(Start Time-out) bit at 1.
Obtain a periodic interrupt while no character is received. This is performed by writing
US_CR with the RETTO (Reload and Start Time-out) bit at 1.
Character
Received
STTTO
1
D
Clear
Q
Baud Rate
Clock
Clock
16-bit Time-out
Counter
TO
Load
16-bit
Value
AT91RM3400
0
=
TIMEOUT
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