BS_Serial memory interface
RM0082
300/844
Doc ID 018672 Rev 1
Note:
If EEPROMs are used instead of Flash memories, a read request address should be
(A 1), being ADDRESS the actual target address to be read.
●
Write requests: wrapping bursts are not supported, causing an ERROR response on
HRESP sent back by SMI to AHB master.
●
Bursts must not cross bank boundaries.
●
In case of BUSY transfer, the SMI is held until BUSY is inactive.
SMI-to-MEMORY interface
Acting as a SPI master, the SMI supports a synchronous full-duplex data link with its up to 2
SPI slaves (that is, the serial memory devices).
It follows that each SPI slave must agree with the communication protocol fixed by SMI in
terms of clock polarity (CPOL) and clock phase (CPHA), specifically CPOL = 1 and CPHA =
1 (that is, clock idles high and data are shifted in and out on the rising edge of the clock).
Prior to any operation involving a SPI-compatible off-chip memory device, the related SPI
slave must be selected by SMI (through chip select), then a 1-byte instruction must be sent
by SMI to the selected memory. The set of instructions supported by SMI is given in
15.4 Operation
modes
SMI is allowed to run in two distinct operation modes:
●
Hardware mode (detailed in
), clearing the SW bit in the SMI_CR1
.
●
Software mode (detailed in
), setting the SW bit in the SMI_CR1 register.
Moreover, in both operation modes SMI can work:
●
Either in normal mode, clearing the FAST bit in the SMI_CR1 register, with a frequency
up to 20 MHz (19 MHz at power-on).
●
Or in fast mode, setting the FAST bit in the SMI_CR1 register, with a frequency ranging
from 20 MHz to 50 MHz.
15.4.1 Hardware
mode
Hardware mode is intended to allow SMI to perform read/write requests from any AHB
master, which can directly access the external serial memory.
Table 238.
SMI supported instruction
Opcode
Description
8’h03
Read data bytes.
8’h0B
Read data bytes at high speed.
8’h05
Read status register.
8’h06
Write enable.
8’h02
Page program.
8’hAB
Release from deep power-down.