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6.4
CFM Operation
The CFM registers, subject to the restrictions previously noted, can generally be read and
written (see Section 6.3.4, "Register Descriptions" for details). Reads of the CFM array
occur normally and writes behave according to the setting of the KEYACC bit in CFMCR.
Program, erase, and verify operations are initiated by the CPU. Special cases of user mode
apply when the CPU is in low-power or debug modes and when the MCU boots in master
mode or emulation mode.
6.4.1
Read Operations
A valid read operation occurs whenever a transfer request is initiated by the ColdFire core,
the address is equal to an address within the valid range of the CFM memory space, and the
read/write control indicates a read cycle.
In order to reduce power at low system clock frequencies, the sense amplifier timeout
(SATO) block minimizes the time during which the sense amplifiers are enabled for read
operations. The sense amplifier enable signals to the Flash timeout after approximately
50 ns.
6.4.2
Write Operations
A valid write operation occurs whenever a transfer request is initiated by the ColdFire core,
the address is equal to an address within the valid range of the CFM memory space, and the
read/write control indicates a write cycle.
The action taken on a valid CFM array write depends on the subsequent user command
issued as part of a valid command sequence. Only aligned 32-bit write operations are
allowed to the CFM array. Byte and word write operations will result in a cycle termination
transfer error.
6.4.3
Program and Erase Operations
Read and write operations are both used for the program and erase algorithms described in
this subsection. These algorithms are controlled by a state machine whose timebase is
derived from the CFM module clock via a programmable counter.
The command register and associated address and data buffers operate as a two stage FIFO
so that a new command along with the necessary address and data can be stored while the
previous command is still in progress. This pipelining speeds when programming more
than one longword on a specific row, as the charge pumps can be kept on in between two
programming commands, thus saving the overhead needed to set up the charge pumps.
Buffer empty and command completion are indicated by flags in the CFM user status
register. Interrupts will be requested if enabled.
MOTOROLA
Chapter 6. ColdFire Flash Module (CFM)
CFM Operation
6-17
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