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Row
Column-1
Data 0
Data 1
...
Data n
CLK
(EPI0S31)
CKE
(EPI0S30)
CSn
(EPI0S29)
WEn
(EPI0S28)
RASn
(EPI0S19)
CASn
(EPI0S18)
DQMH, DQML
(EPI0S [17:16])
AD [15:0]
(EPI0S [15:0])
Activate
NOP
Write
Burst
Term
AD [15:0] driven out
AD [15:0]
driven out
CAS Latency = 2
Initialization and Configuration
1095
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
External Peripheral Interface (EPI)
16.4.2.6 Write Cycle
shows a write cycle of n halfwords; n can be any number greater than or equal to 1. The cycle
begins with the Activate command and the row address on the EPI0S[15:0] signals. With the programmed
CAS latency of 2, the Write command with the column address on the EPI0S[15:0] signals follows after 2
clock cycles. When writing to SDRAMs, the Write command is presented with the first halfword of data.
Because the address lines and the data lines are multiplexed, the column address is modified to be
(programmed address -1). During the Write command, the DQMH and DQML signals are high, so no data
is written to the SDRAM. On the next clock, the DQMH and DQML signals are asserted, and the data
associated with the programmed address is written. The Burst Terminate command occurs during the
clock cycle following the write of the last halfword of data. The WEn, DQMH, DQML, and CSn signals are
deasserted after the last halfword of data is received, signaling the end of the access. At least one clock
period of inactivity separates any two SDRAM cycles.
Figure 16-4. SDRAM Write Cycle
16.4.3 Host Bus Mode
Host Bus supports the traditional 8-bit and 16-bit interfaces popularized by the 8051 devices and SRAM
devices, as well as PSRAM and NOR Flash memory. This interface is asynchronous and uses strobe pins
to control activity. Addressable memory can be doubled using Host Bus-16 mode as it performs halfword
accesses. The EPI0S0 is the LSB of the address and is equivalent to the internal Cortex-M4 A1 address.
EPI0S0 should be connected to A0 of 16-bit memories.
16.4.3.1 Control Pins
The main three strobes are Address Latch Enable (ALE), Write (WRn), and Read (RDn, sometimes called
OEn).The polarity of the read and write strobes can be active-high or active-low by clearing or setting the
RDHIGH and WRHIGH bits in the EPI Host-Bus n Configuration (EPIHBnCFGn) register.
The ALE can be changed to an active-low chip select signal, CSn, through the EPIHBnCFGn register. The
ALE is best used for Host-Bus muxed mode in which EPI address and data pins are shared. All Host-Bus
accesses have an address phase followed by a data phase. The ALE indicates to an external latch to
capture the address then hold it until the data phase. The polarity of the ALE can be active High or Low by
clearing or setting the ALEHIGH bit in the EPI Host-Bus n Configuration (EPIHBnCFGn) register. CSn is
best used for Host-Bus unmuxed mode in which EPI address and data pins are separate. The CSn
indicates when the address and data phases of a read or write access are occurring. Both the ALE and