VR4102 datasheet(686/701 Pages) NEC

686 / 701 page

APPENDIX A DIFFERENCES BETWEEN VR4102 AND VR4101

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A.2 DETAILS OF DIFFERENCES

A.2.1 CPU Core

(1) Cache Size

The instruction cache of the VR4102 is 4K bytes in size, on the other hand, that of the VR4101 is 2K bytes. The

size of the data cache of the VR4102 is 1K bytes which is the same as that of the VR4101.

To specify cache data address used for CACHE instruction, the VR4102 uses bit 31..12 of the TagLo register, in

contrast to the VR4101 which uses bit 31..11. For data cache, both the VR4102 and the VR4101 use bit 13..10 of

the TagLo register.

(2) Settings of the Config Register

Bit 12 of the Config register (CS) indicates cache size mode, bit 11..9 (IC) indicates instruction cache size, and

bit 8..5 (DC) indicates data cache size. In the VR4102, CS is set to 1 (cache of small capacity), IC to 010 (4K

bytes), and DC to 000 (1K bytes). In the VR4101, bit 12..5 of the Config register are not defined and fix to 0 as a

reserved field.

Bit 27..24 of the Config register (EP) indicates transfer data pattern in the cache writeback. This field must be set

to 0000 (DD) in the VR4102, on the other hand, it must be set to 0011 (DxDx) in the VR4101.

A.2.2 Address Mapping

(1) Memory Area

In the VR4102, 16M and 64M bits are selectable for DRAM space size, though only a 16M-bit DRAM can be

connected to the VR4101.

Similarly, 32M and 64M bits are selectable for ROM space size in the VR4102, though only a 32M-bit ROM can

be connected to the VR4101.

(2) LCD Space

The LCD space is mapped to 16M-byte area of 0x0A00 0000 through 0x0AFF FFFF in both the VR4102 and the

VR4101. However, the VR4102 can also use this area as the high speed memory space, and the switching is set

in one of the BCU registers.

(3) ISA Spaces

The ISA memory and I/O spaces have a size of 64M bytes respectively in the VR4102. Those in the VR4101

have 4M bytes in total (2M bytes for 8-bit bus, 2M bytes for 16-bit bus).

In addition, the VR4102 supports 16/8-bit dynamic sizing for the ISA bus.

(4) Internal I/O Space

The internal I/O space is expanded to 32M bytes in the VR4102 compared to that of the VR4101 which has a size

of 16M bytes.

VR4102 Datasheet(PDF) 686 Page - NEC