RM0082
BS_Serial memory interface
Doc ID 018672 Rev 1
307/844
[28]
SW
1’h0
RW
Software mode.
Setting this bit, the software operation mode of SMI is
enabled (
), otherwise (bit cleared, default), the
hardware operation mode is enabled.
[27:26]
ADD_LE
NGTH
2’h0
RW
Address length.
This is a 2 bit field where each bit is associated to a specific
external memory bank, specifically the LSB (bit [24]) refers
to bank0. In particular, each bit states the length of the
address following the instruction opcode issued by SMI to
the relevant bank, according to encoding:
1‘b0 = 3 bytes (default)
1‘b1 = 2 bytes (for EEPROM compliance)
[25:24]
-
-
-
Not Used
[23:16]
HOLD
8’h0
RW
Clock hold period selection.
This 8 bit field states the hold period (where SMI_CK is
stopped while chip select remains active) between bytes as
an integer number of SMI_CK periods (t
SMI_CK
,
[15]
FAST
1’h0
RW
Fast read mode.
This bit provides for mode selection during reading
operation. As specified in
, setting this bit a
clock frequency up to 50 MHz is available, otherwise (bit
cleared) it is reduced to 20 MHz.
[14:08]
PRESC
7’h0
RW
Prescaler value.
This 7 bit field allows to set the prescaler value used to
generate the SMI_CK clock by adjusting the AHB bus
fequency, as detailed in
Note: The SMI_CK frequency is actually changed after the
completion of ongoing transfer.
[07:04]
TCS
4’h5
RW
Deselect time.
This 4 bit field enables to configure the deselect time, that is
the minimum interval lasting between release of chip select
signal and next selection. That is, chip select signal
remains released (not selected) for at least (TCS + 1)
SMI_CK clock periods.
Actual deselect time at power-on reset depends on TCS
reset value (4’h5) and it is limited by the SMI_CK frequency
at power-on reset, that is 19 MHz, resulting in t
SMI_CK
=
52.6 ns. It follows that, at reset, t
cs
= (5+1) · 52.6 ns = 316
ns.
Note: FAST and TCS fields must be written at the same
time as PRESC. All these values are taken into account
after the completion of the ongoing transfer. Any check of
the consistency among these three values has to be done
by software.
Table 241.
SMI_CR1 register bit assignments (continued)
Bit
Name
Reset
value
Type
Description