374
Table 13.9
SMR and SCR Settings and SCI Clock Source Selection
SMR
SCR Settings
SCI Transmit/Receive Clock
Mode
Bit 7:
C/
A
Bit 1:
CKE1
Bit 0:
CKE0
Clock Source
SCK Pin Function
*
Asynchronous
0
0
0
Internal
SCI does not use the SCK pin
mode
1
Outputs a clock with frequency
matching the bit rate
1
0
External
Inputs a clock with frequency 16
times the bit rate
1
Synchronous
1
0
0
Internal
Outputs the serial clock
mode
1
1
0
External
Inputs the serial clock
1
Note:
*
Select the function in combination with the pin function controller (PFC).
13.3.2
Operation in Asynchronous Mode
In asynchronous mode, each transmitted or received character begins with a start bit and ends with
a stop bit. Serial communication is synchronized one character at a time.
The transmitting and receiving sections of the SCI are independent, so full duplex communication
is possible. The transmitter and receiver are both double buffered, so data can be written and read
while transmitting and receiving are in progress, enabling continuous transmitting and receiving.
Figure 13.2 shows the general format of asynchronous serial communication. In asynchronous
serial communication, the communication line is normally held in the mark (high) state. The SCI
monitors the line and starts serial communication when the line goes to the space (low) state,
indicating a start bit. One serial character consists of a start bit (low), data (LSB first), parity bit
(high or low), and stop bit (high), in that order.
When receiving in asynchronous mode, the SCI synchronizes on the falling edge of the start bit.
The SCI samples each data bit on the eighth pulse of a clock with a frequency 16 times the bit rate.
Receive data is latched at the center of each bit.
Summary of Contents for HD6417032
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Page 525: ...490 CK RAS CAS TRp TRc TRcc tRASD1 tRASD2 tCASD3 tCASD2 TRr tCSR Figure 20 18 Self Refresh ...
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