GD32F20x User Manual
681
25.3.
Function overview
25.3.1.
Block diagram
EXMC is the combination of six modules: The AHB bus interface, EXMC configuration
registers, NOR/PSRAM controller, NAND/PC Card controller, SDRAM controller and external
device interface. AHB clock (HCLK) is the reference clock.
Figure 25-1. The EXMC block diagram
AHB Bus Interface
EXMC Configuration
Register
NAND-Flash/PC Card
Controller
NOR-Flash/PSRAM
Controller
EX
M
C
_
CD
E
X
M
C
_N
R
EG
EX
M
C
_N
IO
R
D
EX
M
C
_IN
T
R
EX
M
C
_N
C
E[
2
:1
]
EX
M
C
_N
W
E
EX
M
C
_N
C
E3
_1
EX
M
C
_
IN
T
[2
:1
]
E
X
M
C
_N
W
A
IT
EX
M
C
_
N
C
E3
_0
E
X
M
C
_N
O
E
EX
M
C
_N
IO
W
R
E
X
M
C
_C
LK
EX
M
C
_NL
(o
r
N
A
D
V
)
EX
M
C
_A
[25
:0
]
EX
M
C
_NE
[3
:0
]
E
X
M
C
_N
B
L[
1
:0
]
EX
M
C
_D
[31
:0
]
PC Card
Pins
NAND
Pins
HCLK
from clock
controller
EXMC
interrupt
to NVIC
NOR/PSRAM
Pins
SDRAM
Controller
EX
M
C
_S
D
C
K
E[
1
:0
]
EX
M
C
_S
D
N
E[
1
:0
]
EX
M
C
_S
D
N
R
A
S
EX
M
C
_S
D
N
CA
S
E
X
M
C
_S
D
N
W
E
E
X
M
C
_S
D
C
LK
PSRAM/
SDRAM
Shared
Pin
SDRAM
Pins
Shared
Pins
NOR/PSRAM
/NAND
Shared Pin
EX
M
C
_
N
IO
S16
25.3.2.
Basic regulation of EXMC access
EXMC is the conversion interface between AHB bus and external device protocol. 32-bit of
AHB read/write accesses can be split into several consecutive 8-bit or 16-bit read/write
operations respectively. In the process of data transfer, AHB access data width and memory
data width
may not be the same. In order to ensure consistency of data transmission, EXMC’s
read/write accesses follow the following basic regulation.
When the width of AHB bus equals to the memory bus width. No conversion is applied.
When the width of AHB bus is greater than memory bus width. The AHB accesses are
Summary of Contents for GD32F20 Series
Page 191: ...GD32F20x User Manual 191 Bits Fields Descriptions 31 0 TRNDATA 31 0 32 Bit Random data ...
Page 290: ...GD32F20x User Manual 290 conversion is ongoing ...
Page 325: ...GD32F20x User Manual 325 15 0 ALRM 15 0 RTC alarm value low ...
Page 385: ...GD32F20x User Manual 385 ...
Page 523: ...GD32F20x User Manual 523 clears AERR bit by writing 0 to it ...