NEC uPD72257, Preliminary User'S Manual

Page: 150 / 343

5.7.2.7 HOSTADBASEn - ADBus base registers
These registers set the base address for accesses through the ADBus interface
and controls the word combining function.
Access These registers can be read/written in 16-bit and 32-bit units.
If these registers are read in 32-bit units the upper bits 31 to 8 return undefined
values. Writing to these bits is ignored.
Address HOSTADBASE0: 0000 0020
H
, HOSTADBASE1: 0000 0024
H
HOSTADBASE2: 0000 0028
H
, HOSTADBASE3: 0000 002C
H
Initial Value HOSTADBASE0: 0001
H
, HOSTADBASE1: 0011
H
HOSTADBASE2: 0021
H
, HOSTADBASE3: 0031
H
These registers are initialized by any reset.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 0 BASEADDR[8:0] 0 0 0 WC
R R R R/W R R R R/W
Writing to the read-only bits is ignored, reading returns undefined values.
Caution
The default value "000000000
B
" of HOSTBASE0.BASEADDR[8:0] must not be
changed.
Bit Bit name Function
12 to 4 BASEADDR[8:0]
These bits define the address bits ADADD[27:19] when calculating the internal address
for AHB accesses.
0 WC
Enables the word combining function for this address range, i.e. two consecutive 16-bit
accesses are combined and processed as one 32-bit access.
0 disable word combining
1 enable word combining
Chapter 5 Host CPU Interface
150
Preliminary User's Manual S19203EE1V3UM00