71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
Optical Interface
The device includes an interface to implement an IR/optical port. The pin OPT_Tx is designed to directly drive an external LED
for transmitting data on an optical link. The pin OPT_RX is designed to sense the input from an external photo detector used
as the receiver for the optical link. These two pins are connected to a dedicated UART port (UART1).
The OPT_TX and OPT_RX pins can be inverted with configuration bits OPT_TXINV and OPT_RXINV, respectively.
Additionally, the OPT_TX output may be modulated at 38kHz. Modulation is available when system power is present (i.e. not
in BROWNOUT mode). The OPT_TXMOD bit enables modulation. Duty cycle is controlled by OPT_FDC[1:0], which can select
50%, 25%, 12.5%, and 6.25% duty cycle. 6.25% duty cycle means OPT_TX is low for 6.25% of the period. Figure 7 illustrates
the OPT_TX generator.
V3P3
Internal
VARPULSE
WPULSE
DIO2
3
2
1
OPT_TX
MOD
from OPT_TX UART
A
B
0
OPT_TXINV
EN
DUTY
OPT_TXE[1:0]
OPT_TXMOD
OPT_FDC
2
OPT_TXMOD=1,
OPT_TXMOD=0
OPT_FDC=2 (25%)
A
A
B
B
1/38kHz
Figure 7: Optical Interface
When not needed for the optical UART, the OPT_TX pin can alternatively be configured as DIO2, WPULSE, or VARPULSE.
The configuration bits are OPT_TXE[1:0]. Likewise, OPT_RX can alternately be configured as DIO_1. Its control is OPT_RXDIS.
Digital I/O
The device includes up to 18 pins (QFN 68 package) or 14 pins (LQFP 64 package) of general purpose digital I/O. These pins
are compatible with 5V inputs (no current-limiting resistors are needed). Some of them are dedicated DIO (DIO3), some are
dual-function that can alternatively be used as LCD drivers (DIO4-11, 14-17, 19-21) and some share functions with the optical
port (DIO1, DIO2). On reset or power-up, all DIO pins are inputs until they are configured for the desired direction under MPU
control. The pins are configured by the DIO registers and by the five bits of the LCD_NUM register (located in I/O RAM). Once
declared as DIO, each pin can be configured independently as an input or output with the DIO_DIRn bits. A 3-bit configuration
word, DIO_Rx, can be used for certain pins, when configured as DIO, to individually assign an internal resource such as an
interrupt or a timer control. Table 54 lists the direction registers and configurability associated with each group of DIO pins.
Table 55 shows the configuration for a DIO pin through its associated bit in its DIO_DIR register.
Tables showing the relationship between LCD_NUM and the available segment/DIO pins can be found in the Applications
section and in the I/O RAM Description under LCD_NUM[4:0].
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