Host Access Sequences
7-26
Table 7–16. Write Access to HPI With Autoincrement: HWOB = 0
{
Value During Access
Value After Access
Event
HD
HBE
[1:0]
HR/W
HCNTL
[1:0]
HRDY
HHWIL
HPIC
HPIA
HPID
Location
80001234
Location
80001238
Host writes
HPID
1st halfword
Waiting for
previous access
to complete
wxyz
11
0
10
1
0
00000000
80001234
????????
00000000
00000000
Host writes HPID
1st halfword
Ready
wxyz
11
0
10
0
0
00080008
80001234
wxyz???
00000000
00000000
Host writes HPID
2nd halfword
5566
00
0
10
0
1
00080008
80001234
wxyz5566
00000000
00000000
Host writes HPID
1st halfword
Waiting for
previous access
to complete
33rs
01
0
10
1
0
00000000
80001234
wxyz5566
00005566
00000000
Host writes HPID
1st halfword
33rs
01
0
10
0
0
00080008
80001238
33rs5566
00005566
00000000
Host writes HPID
2nd halfword
nopq
11
0
10
0
1
00080008
80001238
33rsnopq
00005566
00000000
Waiting for
access to
complete
????
??
?
??
1
?
00000000
80001238
33rsnopq
00005566
33000000
† wxyz, rs, and nopq represent don’t care values on HPID.
Note:
A ? in this table indicates the value is unknown.
7.4.6
Single Halfword Cycles
In normal operation, every transfer must consist of two halfword accesses.
However, to speed operation you can perform single halfword accesses.
These can be useful in performing the following tasks:
-
Writes to and reads from HPIC: In Table 7–7, the entire HPIC was written
to correctly after the first write. When writing the HPIC, the host does not
have to be concerned about HHWIL, nor does it have to perform two con-
secutive writes to both halfwords. Similarly, the host can choose to read
the HPIC only once, because both halves contain the same value.