ade7518 Analog Devices, Inc., ade7518 Datasheet - Page 109

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

To transmit, the eight data bits must be written into the Serial
Port Buffer SFR (SBUF, 0x99). The ninth bit must be written
to TB8 in the Serial Communications Control Register SFR
(SCON, 0x98). When transmission is initiated, the eight data
bits from SBUF are loaded into the transmit shift register (LSB
first). The ninth data bit, held in TB8, is loaded into the ninth
bit position of the transmit shift register. The transmission starts
at the next valid baud rate clock. The transmit interrupt flag (TI)
is set as soon as the transmission completes, when the stop bit
appears on TxD.
All of the following conditions must be met at the time the final
shift pulse is generated to receive a character:
•
•
If any of these conditions are not met, the received frame is
irretrievably lost, and the receive interrupt flag (RI) is not set.
Reception for Mode 2 is similar to that of Mode 1. The eight
data bytes are input at RxD (LSB first) and loaded onto the
receive shift register. If the received frame has met the previous
criteria, the following events occur:
•
•
•
Mode 3 (9-Bit UART with Variable Baud Rate)
Mode 3 is selected by setting both SM0 and SM1. In this mode,
the 8052 UART serial port operates in 9-bit mode with a variable
baud rate. The baud rate is set by a timer overflow rate. Timer 1
or Timer 2 can be used to generate baud rates, or both timers
can be used simultaneously, where one generates the transmit
rate and the other generates the receive rate. There is also a
dedicated timer for baud rate generation, the UART timer,
which has a fractional divisor to precisely generate any baud
rate (see the UART Timer Generated Baud Rates section). The
operation of the 9-bit UART is the same as for Mode 2, but the
baud rate can be varied.
In all four modes, transmission is initiated by any instruction
that uses SBUF as a destination register. Reception is initiated in
Mode 0 when RI = 0 and REN = 1. Reception is initiated in the
other modes by the incoming start bit if REN = 1.
If the extended UART is disabled (EXTEN = 0 in the CFG
SFR), RI must be 0 to receive a character. This ensures that
the data in SBUF is not overwritten if the last received
character has not been read.
If multiprocessor communication is enabled by setting
SM2, the received ninth bit must be set to receive a character.
This ensures that only frames with the ninth bit set, that is,
frames that contain addresses, generate a receive interrupt.
The eight bits in the receive shift register are latched into
the SBUF SFR.
The ninth data bit is latched into RB8 in the SCON SFR.
The receiver interrupt flag (RI) is set.
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UART BAUD RATE GENERATION
Mode 0 Baud Rate Generation
The baud rate in Mode 0 is fixed.
Mode 2 Baud Rate Generation
The baud rate in Mode 2 depends on the value of the PCON[7]
(SMOD) bit in the Program Control SFR (PCON, 0x87). If
SMOD = 0, the baud rate is 1/32 of the core clock. If SMOD = 1,
the baud rate is 1/16 of the core clock.
Mode 1 and Mode 3 Baud Rate Generation
The baud rates in Mode 1 and Mode 3 are determined by the
overflow rate of the timer generating the baud rate, that is,
either Timer 1, Timer 2, or the dedicated baud rate generator,
UART timer, which has an integer and fractional divisor.
Timer 1 Generated Baud Rates
When Timer 1 is used as the baud rate generator, the baud rates
in Mode 1 and Mode 3 are determined by the Timer 1 overflow
rate. The value of SMOD is as follows:
The Timer 1 interrupt should be disabled in this application.
The timer itself can be configured for either timer or counter
operation, in any of its three running modes. In the most typical
application, it is configured for timer operation in autoreload
mode (high nibble of TMOD = 0010 binary). In that case, the
baud rate is given by the following formula:
Timer 2 Generated Baud Rates
Baud rates can also be generated by using Timer 2. Using Timer 2
is similar to using Timer 1 in that the timer must overflow 16 times
before a bit is transmitted or received. Because Timer 2 has a
16-bit autoreload mode, a wider range of baud rates is possible.
Therefore, when Timer 2 is used to generate baud rates, the
timer increments every two clock cycles rather than every core
machine cycle as before. It increments six times faster than
Timer 1, and, therefore, baud rates six times faster are possible.
Because Timer 2 has 16-bit autoreload capability, very low baud
rates are still possible. Timer 2 is selected as the baud rate
generator by setting TCLK and/or RCLK in Timer/Counter 2
Control SFR (T2CON, 0xC8). The baud rates for transmit and
receive can be simultaneously different. Setting RCLK and/or
Mode 1 or Mode 3 Baud Rate =
Mode 1 or Mode 3 Baud Rate =
Mode 1 or Mode 3 Baud Rate =
Mode 0 Bau
Mode
2
SMOD
32
2
×
Baud
Timer 1 Overflow Rate
d Rate
Rate
=
=
⎛
⎜
⎝
2
f
SMOD
32
CORE
12
×
⎞
⎟
⎠
16
f
1
CORE
2
SMOD
32
× Timer 2 Overflow Rate
×
(
256
f
CORE
−
ADE7518
TH1
)