ade7518 Analog Devices, Inc., ade7518 Datasheet - Page 111

• Manufacturer Part Number: ade7518
• Description: Single-phase Energy Measurement Ic With 8052 Mcu, Rtc, And Lcd Driver
• Manufacturer: Analog Devices, Inc.

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:
Note that SBAUDF should be rounded to the nearest integer.
After the values for DIV and SBAUDF are calculated, the actual
baud rate can be calculated with the following formula:
For example, to obtain a baud rate of 9600 bps while operating
at a core clock frequency of 4.096 MHz with the PLL CD bits
equal to 0,
Note that the DIV result is rounded down.
Thus, the actual baud rate is 9570 bps, resulting in a 0.31% error.
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 whether the Rx line has been
low for longer than a 9-bit frame. It indicates that the data just
received, a 0 or null character, is not valid because the master has
disconnected. Overwrite error detection indicates when the
received data has not been read fast enough and, as a 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 prevents
frames without a stop bit from being received. The stop bit is
latched into the RB8 bit in the Serial Communications Control
Register SFR (SCON, 0x98). 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 Enhanced Serial Baud Rate Control
SFR (SBAUDT, 0x9E). The FE bit is set on framing errors for
both 8-bit and 9-bit UARTs.
SBAUDF
DIV
SBAUDF
Actual
+ SBTH
Baud
=
64
=
64
Rate
×
⎛
⎜
⎜
⎝
=
×
16
log
⎛
⎜
⎝
=
×
16
2
16
⎛
⎜
⎝
DIV
, 4
×
4,096,000
16
log
096
×
2
+
2
3
×
SBTH
( )
f
DIV
×
2
CORE
,
9600
000
9600
+
×
SBTH
Baud
⎞
⎟
⎠
f
−
CORE
=
×
1
Rate
⎞
⎟
⎠
⎛ +
⎜
⎝
. 4
1
=
74
42
−
SBAUDF
=
1
.
67
⎞
⎟
⎟
⎠
4
64
=
0x2B
⎞
⎟
⎠
Rev. 0 | Page 111 of 128
The 8052 standard UART does not provide break error detection.
However, for an 8-bit UART, a break error can be detected when
the received character is 0, a null character, and when there is a
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 ADE7518 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 when the receive interrupt
flag, RI, is set. However, it does not indicate if a character has
been lost because the RI bit is set when the frame is received.
The enhanced UART overwrite error detection provides this
information. When the enhanced 8052 UART is enabled, a
frame is 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 is set. The overwrite error flag is
cleared when SBUF is read.
The extended UART is enabled by setting the EXTEN bit in the
Configuration SFR (CFG, 0xAF).
UART TxD Signal Modulation
There is an internal 38 kHz signal that can be OR’ e d 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 RxD pin (see the 3.3 V Peripherals and Wake-Up
Events section).
EXTEN = 1
EXTEN = 1
Rx
FE
Rx
FE
RI
RI
START
START
Figure 94. UART Timing in Mode 2 and Mode 3
D0
D0
Figure 93. UART Timing in Mode 1
D1
D1
D2
D2
D3
D3
D4
D4
D5
D5
D6
D6
D7
ADE7518
D7
D8
STOP
STOP