71M6541D Datasheet, PDF (73/166 Pages) Maxim Integrated Products – 0.1% Accuracy Over 2000:1 Current Range Energy Meter ICs

71M6541D/F/G and 71M6542F/G Data Sheet
EECTRL Byte Written
Write -- No HiZ
SCLK (output)
INT5 not issued
EECTRL Byte Written
CNT Cycles (0 shown)
Write -- HiZ
SCLK (output)
INT5 not issued
CNT Cycles (0 shown)
SDATA (output)
D7
SDATA (output)
SDATA output Z
(LoZ)
SDATA output Z
(HiZ)
BUSY (bit)
BUSY (bit)
Figure 25: 3-Wire Interface. Write Command when CNT=0
EECTRL Byte Written
Write -- With HiZ and WFR
SCLK (output)
CNT Cycles (6 shown)
SDATA (out/in)
SDATA output Z
D7
D6
D5
D4
D3
D2
(From 654x)
(LoZ)
BUSY (bit)
BUSY
(From EEPROM)
(HiZ)
Figure 26: 3-wire Interface. Write Command when HiZ=1 and WFR=1.
INT5
READY
2.5.10 SPI Slave Port
The slave SPI port communicates directly with the MPU data bus and is able to read and write Data RAM
and I/O RAM locations. It is also able to send commands to the MPU. The interface to the slave port
consists of the SPI_CSZ, SPI_CKI, SPI_DI and SPI_DO pins. These pins are multiplexed with the
combined DIO/LCD segment driver pins SEGDIO36 to SEGDIO39.
Additionally, the SPI interface allows flash memory to be read and to be programmed. To facilitate flash
programming, cycling power or asserting RESET causes the SPI port pins to default to SPI mode. The
SPI port is disabled by clearing the SPI_E bit (I/O RAM 0x270C[4]).
Possible applications for the SPI interface are:
1) An external host reads data from CE locations to obtain metering information. This can be used in
applications where the 71M654x function as a smart front-end with preprocessing capability. Since
the addresses are in 16-bit format, any type of XRAM data can be accessed: CE, MPU, I/O RAM, but
not SFRs or the 80515-internal register bank.
2) A communication link can be established via the SPI interface: By writing into MPU memory locations,
the external host can initiate and control processes in the 71M654x MPU. Writing to a CE or MPU
location normally generates an interrupt, a function that can be used to signal to the MPU that the
byte that had just been written by the external host must be read and processed. Data can also be
inserted by the external host without generating an interrupt.
3) An external DSP can access front-end data generated by the ADC. This mode of operation uses the
71M654x as an analog front-end (AFE).
4) Flash programming by the external host (SPI Flash Mode).
SPI Transactions
A typical SPI transaction is as follows. While SPI_CSZ is high, the port is held in an initialized/reset state.
During this state, SPI_DO is held in Hi-Z state and all transitions on SPI_CLK and SPI_DI are ignored.
When SPI_CSZ falls, the port begins the transaction on the first rising edge of SPI_CLK. As shown in
Table 62, a transaction consists of an optional 16 bit address, an 8 bit command, an 8 bit status byte,
followed by one or more bytes of data. The transaction ends when SPI_CSZ is raised. Some transactions
may consist of a command only.