EM78P312N
The figure below shows the general format of one character sent or received. The communication channel is normally held in the marked state (high). Character transmission or reception starts with a transition to the space state (low).
The first bit transmitted or received is the start bit (low). It is followed by the data bits, in which the least significant bit (LSB) comes first. The data bits are followed by the parity bit. If present, then the stop bit or bits (high) confirm the end of the frame.
In receiving, the UART synchronizes on the falling edge of the start bit. When two or three “0” are detected during three samples, it is recognized as normal start bit and the receiving operation is started.
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| Idle state |
START | D0 | D1 | D2 | Dn | Parity | STOP | (mark) |
bit | bit | bit |
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1 bit |
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| 7 or 8 bits |
| 1 bit | 1 bits |
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| One character or frame |
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Fig.
5.7.1 UART Mode
There are three UART modes. Mode 1 (7 bits data) and Mode 2 (8 bits data) allow the addition of a parity bit. The parity bit addition is not available in Mode 3. The Figure below shows the data format in each mode.
| UMODE | PRE | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | |
Mode 1 | 0 | 0 | 0 | START |
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| 7 bits DATA |
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| STOP |
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| 0 | 0 | 1 | START |
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| 7 bits DATA |
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| Parity | STOP | |||
Mode 2 | 0 | 1 | 0 | START |
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| 8 bits DATA |
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| STOP |
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| 0 | 1 | 1 | START |
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| 8 bits DATA |
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| Parity | STOP | ||
Mode 3 | 1 | 0 | X | START |
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| 9 bits DATA |
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| STOP | ||
Fig.
5.7.2 Transmitting
In transmitting serial data, the UART operates as follows:
1.Set the TXE bit of the URC1 register to enable the UART transmission function.
2.Write data into the URTD register and the UTBE bit of the URC1 register will be set by hardware.
Product Specification (V1.0) 10.03.2006 | • 29 |
(This specification is subject to change without further notice)
