ADE5166_08 AD [Analog Devices], ADE5166_08 Datasheet - Page 124

• Manufacturer Part Number: ADE5166_08
• Description: Single-Phase Energy Measurement IC with 8052 MCU, RTC, and LCD Driver
• Manufacturer: AD [Analog Devices]

ADE5166/ADE5169
To transmit, the eight data bits must be written into the serial
port buffer SFR (SBUF, Address 0x99). The ninth bit must be
written to TB8 (Bit 3) in the serial communications control SFR
(SCON, Address 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 serial port transmit
interrupt flag (TI, Bit 1 in the SCON SFR) 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 is not met, the received frame is
irretrievably lost, and the receive interrupt flag (RI in the SCOn
SFR) 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 the SCON
SFR. 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 in the SCON SFR. 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 in the SCON SFR 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 in the SCON SFR, the received ninth bit must be set to
receive a character. This ensures that only frames with the
ninth bit set, which are 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 in the SCON SFR) 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 SMOD
bit in the program control SFR (PCON, Address 0x87[7]). 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,
Timer 1, Timer 2, or the dedicated baud rate generator, UART
timer, which has an integer and a 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 and in any of its three running modes. In the most
typical application, it is configured for timer operation in auto-
reload mode (high nibble of TMOD = 0010 binary, see Table 12).
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.
Mode 2 Baud Rate =
Mode 1 or Mode 3 Baud Rate =
Mode 1 or Mode 3 Baud Rate =
Mode 1 or Mode 3 Baud Rate =
Mode 0 Bau
2
SMOD
32
×
Timer 1 Overflow Rate
d Rate
=
⎛
⎜
⎝
2
f
SMOD
CORE
12
32
⎞
⎟
⎠
× f
16
1
2
CORE
SMOD
32
× Timer 2 Overflow Rate
×
(
256
f
CORE
−
TH1
)