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IDT Device Controller
Theory of Operation
79RC32438 User Reference Manual
6 - 4
November 4, 2002
Notes
Device zero is the boot device and contains the boot exception vector. Since read operations to this
device must take place before software can initialize the system, the DEV0C and DEV0TC registers must
have default values that allow the boot device to be read following a cold reset. Initial values for the DEVxC
and DEVxTC registers for all devices are summarized in Table 6.2. These values may be modified during
system initialization.
The RC32438 only reads data from a memory and peripheral bus device that is actually requested by
the CPU or external DMA. For these transactions, the RC32438 never “reads past” the ending address of a
transaction. For example, if the CPU reads a byte from a Memory and Peripheral Bus address, only that
byte is actually read from memory.
Note:
This is not true for PCI masters and general DMA operations; data may be read past the
ending address of a transaction.
Table 6.2 shows the default values for the device configuration registers.
Register Field
Initial
Value
Description/Comment
DEVxC
DS
Boot
Configuration
Device Size
. Boot configuration vector (Refer to the Boot Configuration
Vector section in Chapter 3).
BE
0x1
Buffer Enable.
Initial value places the boot device on buffered data bus.
WP
0x1
Write Protect.
Initial value disables writes to the boot device.
BRE
0x0
Burst Read Enable.
Burst reads are disabled from the boot device.
BWE
0x0
Burst Write Enable.
Burst writes are disabled to the boot device.
RWS
0x3F
Read Wait States.
Initially configured for maximum number of wait states.
WWS
0x3F
Write Wait States.
Initially configured for maximum number of wait states.
WAM
0x0
Wait/Ack Mode.
Initially configured for wait mode.
CSD
0xF
Chip Select Delay.
Initially configured for maximum delay.
OED
0xF
Output Enable Delay.
Initially configured for maximum delay.
BWD
0xF
Byte Write Enable Delay.
Initially configured for maximum delay.
DEVxTC
PRD
0xF
Postread Delay.
Initially configured for maximum delay.
PWD
0xF
Postwrite Delay.
Initially configured for maximum delay.
WDH
0x7
Write Data Hold.
Initially configured for maximum delay.
CSH
0x3
Chip Select Hold.
Initially configured for maximum delay.
Table 6.2 Default Values for Device Configuration Registers