GD32F20x User Manual
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needed, software must clear the EXMC_NECCx register value by resetting ECCEN bit of
EXMC_NPCTLx register to zero, and then restart ECC calculation by setting the ECCEN bit
of EXMC_NPCTLx to one.
PC/CF card access
EXMC Bank3 is used exclusively for PC/CF Card, both memory and IO mode access are
supported. This bank is divided further into three sub spaces, memory, attribute and IO space.
EXMC_NCE3_0 and EXMC_NCE3_1 are the byte select signals, when only EXMC_NCE3_0
is active (Low), the lower byte or upper byte is selected depending on the EXMC_A[0], while
only EXMC_NCE3_1 is active (Low), the upper byte is selected which is not supported, when
both of these signals are active, 16-bit operation is performed. When NDTP is reset to select
PC/CF Card as external memory device, NDW must be set to 01 in EXMC_NPCTLx register
to guarantee correct EXMC operation.
EXMC PC/CF card access behavior for different spaces:
Common space: EXMC_NCE3_x (x = 0, 1) is the chip enable signal, it indicates whether
8- or 16-bit access operation is being performed. EXMC_NWE and EXMC_NOE dictates
whether the on-going operation is a write or read operation, and EXMC_NREG is high
during common space access.
Attribute space: EXMC_NCE3_x (x = 0, 1) is the chip enable signal, it indicates whether
8- or 16-bit access operation is being performed. EXMC_NWE and EXMC_NOE dictates
whether the on-going operation is a write or read operation, and EXMC_NREG is low
during attribute space access.
IO space: EXMC_NCE3_x (x = 0, 1) is the chip enable signal, it indicates whether 8- or
16-bit access operation is being performed. EXMC_NIOWR and EXMC_NIORD dictates
whether the on-going operation is a write or read operation, and EXMC_NREG is low
during IO space access.
AHB access on 16-bit PC/CF card:
1.
Common space: It is usually where data are stored, it could be accessible either in byte
or in half-word mode, and odd address access is not supported in byte mode. When AHB
word access is selected, EXMC automatically splits it into 2 consecutive half-word
access. EXMC_NREG is high when common memory is targeted. EXMC_NOE and
EXMC_NWE are the read and write enable signal for this type of access.
2.
Attribute space: It is usually where configuration information are stored, for byte AHB
access, only even address is possible. Half-word access converts into a single byte
access automatically, and word access is converted into two consecutive byte access
where only the even bytes are operational. In both half-word and word access, only
EXMC_NCE3_0 will be active. EXMC_NREG is low when attribute memory is targeted.
EXMC_NOE and EXMC_NWE are the read and write enable signal for this type of
access.
Содержание GD32F20 Series
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Страница 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...