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ADE7166 数据表(PDF) 129 Page - Analog Devices |
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ADE7166 数据表(HTML) 129 Page - Analog Devices |
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129 / 148 page  Preliminary Technical Data ADE75xx/ADE71xx Rev. PrE | Page 129 of 148 The appropriate value to write to the DIV[2:0] and SBTH[1:0] bits can be calculated using the following formula where Fcore is defined in POWCON SFR. Note that the DIV value must be rounded down to the nearest integer. DIV+ SBTH = () 2 log 16 log ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ × Rate Baud F core SBAUDF is the fractional divider ratio required to achieve the required baud rate. The appropriate value for SBAUDF can be calculated with the following formula: SBAUDF = ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − × ⋅ ∗ + 1 2 16 64 Rate Baud F SBTH DIV core Note that SBAUDF should be rounded to the nearest integer. Once the values for DIV and SBAUDF are calculated, the actual baud rate can be calculated with the following formula: Actual Baud Rate = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + ⋅ ⋅ + 64 1 2 16 SBAUDF F SBTH DIV core For example, to get a baud rate of 9600 while operating at a core clock frequency of 4.096 MHz, with the PLL CD bits equal to zero, DIV + SBTH = log(4096000/(16 × 9600))/log2 = 4.74 = 4 Note that the DIV result is rounded down. SBAUDF = 64*(4096000/(16*23*9600)-1) = 42.67 = 2BH Therefore, the actual baud rate is 9570 bps, which gives an error of 0.31%. UART ADDITIONAL FEATURES Enhanced Error Checking The extended UART provides frame error, break error and overwrite error detection. Framing errors occur when a stop bit is not present at the end of the frame. A missing stop bit implies that the data in the frame may not have been received properly. Break error detection indicates if the Rx line has been low for longer than a 9-bit frame. It indicates that the data just received, a zero, or NUL character, is not valid because the master has disconnected. Overwrite error detection indicates if the received data isn’t read fast enough and as result, a byte of data has been lost. The 8052 standard UART offers frame error checking for an 8- bit UART through the SM2 and RB8 bits. Setting the SM2 bit prevent frames without a stop bit from being received. The stop bit is latched into the RB8 bit in the SCON register. This bit can be examined to determine if a valid frame was received. The 8052 does not however, provide frame error checking for a 9-bit UART. This enhanced error checking functionality is available through the frame error bit, FE in the SBAUDT SFR. The FE bit will be set on framing errors for both 8-bit and 9-bit UARTs. RX D0 D1 D2 D3 D4 D5 D6 D7 START STOP RI FE EXTEN=1 Figure 80: UART Timing in Mode 1 RX D0 D1 D2 D3 D4 D5 D6 D7 START STOP D8 RI FE EXTEN=1 Figure 81: UART Timing in Modes 2 and 3 The 8052 standard UART does not provide break error detection. However for an 8-bit UART, it can be determined that a break error occurred if the received character is zero, a NUL character, and there was no stop bit because the RB8 bit is low. Break error detection is not possible for a 9-bit 8052 UART because the stop bit is not recorded. The ADE75XX/ADE71XX enhanced break error detection is available through the BE bit in the SBAUDT SFR. The 8052 standard UART prevents overwrite errors by not allowing a character to be received if the RI, receive interrupt flag, is set. However, it does not indicate if a character has been lost because the RI bit was set when the frame was received. The enhanced UART overwrite error detection provides this information. When the enhanced 8052 UART is enabled, a frame will be received regardless of the state of the RI flag. If RI=1 when a new byte is received, the byte in SCON is overwritten, and the overwrite error flag will be set. The overwrite error flag will be cleared when SBUF is read. The extended UART is enabled by setting the EXTEN bit in the CFG SFR. UART TxD signal modulation There is an internal 38 kHz signal which can be ORed with the UART transmit signal for use in remote control applications— see the 38 kHz Modulation section. One of the events that can wake the MCU from sleep mode is activity on the UART RX pin—see the 3.3V Peripherals and Wakeup Events section. |
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