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GD32F20x User Manual
717
2.
Timing parameter specification: SDRAM timing configuration register EXMC_SDTCFGx
should be programed according to external SDRAM data sheet for SDRAM controller to
keep pace with the operation of the external SDRAM. RPD and ARFD must be
programed in EXMC_SDTCFG0, those corresponding bit position in EXMC_SDTCFG1
are reserved.
3.
Enable SDCLK: SDCLK enable command should be issued to the corresponding
SDRAM devices, this is done by writing 0b001 to the CMD bits in the EXMC_SDCMD
register, DS0 and DS1 selected which device will accept the command and start
receiving EXMC_SDCLK.
4.
Power-up delay: typical delay is around 100us.
5.
Precharge all: A precharge all command should be issued to reset all the SDRAM
memory banks to their idle state, waiting for subsequent operation. This is done by writing
0b010 to the CMD bits in the EXMC_SDCMD register, DS0 and DS1 defines which
SDRAM device will receive this command.
6.
Set auto-refresh: Auto-refresh command is sent by writing 0b011 in the CMD bits in
EXMC_SDCMD register. Users should also specify the number of consecutive refresh
command to issue each time by configuring the NARF bits, this configuration is
requested by SDRAM specification, it is also where users should refer to.DS0 and DS1
defines which SDRAM device will receive this command.
7.
Mode register configuration: Mode register is programed by writing the mode register
content in MRC bits in EXMC_SDCMD register, mode register specifies the operating
mode of SDRAM, such modes include burst length, burst type, CAS latency, and write
mode. Users should refer to the SDRAM’s specification for correct configuration. CAS
latency should be the same as the CL bits in EXMC_SDCTLx register, and burst length
of 1 must be selected, otherwise S
DRAMC’s behavior is not guaranteed. If the mode
register contents are different for both SDRAM devices, this step should be repeated,
targeting one device a time by the DS0 and DS1 configuration.
8.
Set auto-refresh rate: Auto-refresh rate corresponds to the time between refresh cycles,
users must ensure that this time period match that of the SDRAM specification.
Now SDRAMC is ready to proceed with memory access. If system reset happens, the
initialization sequence must be repeated. Initialization must be performed at least once before
SDRAM read/write access.
Precharge
When the memory controller needs to access a different row, it must first return that bank
’s
sense amplifiers to an idle state, ready to sense the next row. This is known as a precharge
operation, or deactivating the row. A precharge may be commanded explicitly by the
precharge all command, or it may performed automatically at the conclusion of a read or write
operation. There is a minimum time, the row precharge delay (RPD), which must elapse
before that banks is fully idle and it may receive another activate command.
Содержание GD32F20 Series
Страница 1: ...GigaDevice Semiconductor Inc GD32F20x ARM Cortex M3 32 bit MCU User Manual Revision 2 2 Oct 2019 ...
Страница 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Страница 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Страница 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
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Страница 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...