APPENDIX A DIFFERENCES BETWEEN V
R
4102 AND V
R
4101
686
A.2 DETAILS OF DIFFERENCES
A.2.1 CPU Core
(1) Cache Size
The instruction cache of the V
R
4102 is 4K bytes in size, on the other hand, that of the V
R
4101 is 2K bytes. The
size of the data cache of the V
R
4102 is 1K bytes which is the same as that of the V
R
4101.
To specify cache data address used for CACHE instruction, the V
R
4102 uses bit 31..12 of the TagLo register, in
contrast to the V
R
4101 which uses bit 31..11. For data cache, both the V
R
4102 and the V
R
4101 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 V
R
4102, CS is set to 1 (cache of small capacity), IC to 010 (4K
bytes), and DC to 000 (1K bytes). In the V
R
4101, 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 V
R
4102, on the other hand, it must be set to 0011 (DxDx) in the V
R
4101.
A.2.2 Address Mapping
(1) Memory Area
In the V
R
4102, 16M and 64M bits are selectable for DRAM space size, though only a 16M-bit DRAM can be
connected to the V
R
4101.
Similarly, 32M and 64M bits are selectable for ROM space size in the V
R
4102, though only a 32M-bit ROM can
be connected to the V
R
4101.
(2) LCD Space
The LCD space is mapped to 16M-byte area of 0x0A00 0000 through 0x0AFF FFFF in both the V
R
4102 and the
V
R
4101. However, the V
R
4102 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 V
R
4102. Those in the V
R
4101
have 4M bytes in total (2M bytes for 8-bit bus, 2M bytes for 16-bit bus).
In addition, the V
R
4102 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 V
R
4102 compared to that of the V
R
4101 which has a size
of 16M bytes.