Bus Width Of External Bus Interface - NEC V850E/MA1 Application Note

3.7 Bus Width of External Bus Interface

The operation mode of the data bus with respect to the external bus interface can be changed via the I_MODE16
pin status.
Cautions 1. Do not change the status of the I_MODE16 pin during operation.
2. The I_MODE16 pin can only be used to change the operation mode of the data bus with
respect to the external bus slave interface.
To change the data bus width of the SDRAM bus interface, use the BUS_SIZE bit in 3.4.10
SDRAM_CTL register.
3. The setting of the I_MODE16 pin should correspond with the external bus interface operation
mode of the CPU.
4. When 16-bit mode is set, the access cycle is divided for 32-bit access on the external bus
interface. Accordingly, access is divided similarly on the PCI bus interface. Therefore, when
16-bit mode is set, because a 32-bit access cycle is not generated on the PCI bus interface, a
PCI device whose registers are only valid for 32-bit access cannot be accessed.
Table 3-4. I_MODE16 Pin Status and Operation Mode of Data Bus
I_MODE16 Pin
Low level
High level
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CHAPTER 3 SPECIFICATIONS OF PCI HOST BRIDGE MACRO
Data Bus Operation Mode
32-bit mode
16-bit mode
Application Note U17121EJ1V1AN
Remark
32-bit data bus
16-bit data bus