CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U12688EJ4V0UM00
297
(3) Reception
If reception is enabled, sampling of the RXDn pin is started and if a start bit is detected, data reception begins.
When 1 frame of data reception is completed, the reception complete interrupt (INTSRn) is generated.
Normally, with this interrupt processing, receive data is transmitted from the receive buffer (RXBn or RXBnL)
to memory (n = 0, 1).
(a) Receive enabled state
Reception is enabled when the RXEn bit of the ASIMn0 register is set to 1.
RXEn = 1: Receive enabled state
RXEn = 0: Receive disabled state
However, when reception is enabled, be sure to set both the CTXEn and CRXEn bits of the clocked serial
interface mode register (CSIMn) of the channel in use to 0.
In the receive disabled state, the reception hardware stands by in the initial state.
At this time, no reception complete interrupts or reception error interrupts are generated, and the contents
of the receive buffer are retained.
(b) Start of receive operation
The receive operation is started by detection of the start bit.
The RXDn pin is sampled using the serial clock from the baud rate generator (BRGn). When an RXDn
pin low level is detected, the RXDn pin is sampled again after 8 serial clock cycles. If it is low this is
recognized as a start bit, the receive operation is started and the RXDn pin input is subsequently sampled
at intervals of 16 serial clock cycles.
If the RXDn pin input is found to be high when sampled again 8 serial clock cycles after an RXDn pin low
level is detected, this low level is not recognized as a start bit, the operation is stopped by initializing the
serial clock counter for sample timing generation, and the unit waits for the next low-level input.
(c) Reception complete interrupt request
When RXEn = 1, after one frame of data has been received, the receive data in the shift register is
transferred to RXBn and RXBnL a reception complete interrupt request (INTSRn) is generated.
Also, even if an error occurs, the receive data where the error occurred is transmitted to the receive buffer
(RXBn or RXBnL) and a reception complete interrupt (INTSRn) and receive error interrupt (INTSERn) are
generated simultaneously.
Furthermore, if the RXEn bit is reset (0) during a receive operation, the receive operation is stopped
immediately. At this time, the contents of the receive buffer (RXBn or RXBnL) and the asynchronous
serial interface status register (ASISn) do not change and the reception complete interrupt (INTSRn) and
receive error interrupt (INTSERn) are not generated.
When RXEn = 0 and reception is disabled, a reception complete interrupt request is not generated.
Содержание V850E/MS1 UPD703100
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