71M6545 Datasheet, PDF (63/134 Pages) Maxim Integrated Products – Four-Quadrant Metering, Phase Metrology Processors Flash/RAM Size

PDS_6545_009
Data Sheet 71M6545/H
In SFM mode, the 71M6545/H supports n byte reads and dual-byte writes to flash memory. See the SPI
Transaction description on Page 60 for the format of read and write commands. Since the flash write
operation is always based on a two-byte word, the initial address must always be even. Data is written to
the 16-bit flash memory bus after the odd word is written.
In SFM mode, the MPU is completely halted. For this reason, the interrupt feature described in the SPI
Transaction section above is not available in SFM mode. The 71M6545/H must be reset by the WD timer or
by the RESET pin in order to exit SFM mode.
Invoking SFM
The following conditions must be met prior to invoking SFM:
• ICE_E = 1. This disables the watchdog and adds another layer of protection against inadvertent
Flash corruption.
• The external power source (V3P3SYS, V3P3A) is at the proper level (> 3.0 VDC).
• PREBOOT = 0 (SFR 0xB2[7]). This validates the state of the SECURE bit (SFR 0xB2[6]).
• SECURE = 0. This I/O RAM register indicates that SPI secure mode is not enabled. Operations are
limited to SFM Mass Erase mode if the SECURE bit = 1 (Flash read back is not allowed in Secure mode).
• FLSH_UNLOCK[3:0] = 0010 (I/O RAM 0x2702[7:4]).
The I/O RAM registers SFMM (I/O RAM 0x2080) and SFMS (I/O RAM 0x2081) are used to invoke SFM. Only
the SPI interface has access to these two registers. This eliminates an indirect path from the MPU for
disabling the watchdog. SFMM and SFMS need to be written to in sequence in order to invoke SFM. This
sequential write process prevents inadvertent entering of SFM. The sequence for invoking SFM is:
• First, write to SFMM (I/O RAM 0x2080) register. The value written to this register defines the SFM mode.
o 0xD1: Mass Erase mode. A Flash Mass erase cycle is invoked upon entering SFM.
o 0x2E: Flash Read back mode. SFM is entered for Flash read back purposes. Flash writes
are blocked and it is up to the user to guarantee that only previously unwritten locations are
written. This mode is not accessible when SPI secure mode is set.
o SFM is not invoked if any other pattern is written to the SFMM register.
• Next, write 0x96 to the SFMS (I/O RAM 0x2081) register. This write invokes SFM provided that the
previous write operation to SFMM met the requirements. Writing any other pattern to this register
does not invoke SFM. Additionally, any write operations to this register automatically reset the
previously written SFMM register values to zero.
SFM Details
The following occurs upon entering SFM.
• The CE is disabled.
• The MPU is halted. Once the MPU is halted it can only be restarted with a reset. This reset can be
accomplished with the RESET pin, a watchdog reset, or by cycling power.
• The Flash control logic is reset in case the MPU was in the middle of a Flash write operation or Erase
cycle.
• Mass erase is invoked if specified in the SFMM (I/O RAM 0x2080) register (see Invoking SFM, above).
The SECURE bit (SFR 0xB2[6]) is cleared at the end of this and all Mass Erase cycles.
• All SPI read and write operations now refer to Flash instead of XRAM space.
The SPI host can access the current state of the pending multi-cycle Flash access by performing a 4-byte
SPI write of any address and checking the status field.
All SPI write operations in SFM mode must be 6-byte write transactions that write two bytes to an even
address. The write transactions must contain a command byte of 0x00 which is the form that does not
create an MPU interrupt. Auto incrementing is disabled for write operations.
SPI read transactions can make use of auto increment and may access single bytes. The command byte
must always be 0x80 in SFM read transactions.
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