Motorola MVME172 用户手册
LCSR Programming Model
http://www.mcg.mot.com/literature
2-55
2
Local Bus to VMEbus Requester Control Register
This register controls the VMEbus request level, the request mode, and
release mode for the local bus to VMEbus interface.
release mode for the local bus to VMEbus interface.
LVREQL
These bits define the VMEbus request level. The request
is only changed when the VMEchip2 is bus master. The
VMEchip2 always requests at the old level until it
becomes bus master and the new level takes effect. If the
VMEchip2 is bus master when the level is changed, the
new level does not take effect until the bus has been
released and re-requested at the old level. The requester
always requests the VMEbus at level 3 the first time
following a SYSRESET.
is only changed when the VMEchip2 is bus master. The
VMEchip2 always requests at the old level until it
becomes bus master and the new level takes effect. If the
VMEchip2 is bus master when the level is changed, the
new level does not take effect until the bus has been
released and re-requested at the old level. The requester
always requests the VMEbus at level 3 the first time
following a SYSRESET.
0
The request level is 0.
1
The request level is 1.
2
The request level is 2.
3
The request level is 3.
LVRWD
When this bit is high, the requester operates in the
release-when-done mode. When this bit is low, the
requester operates in the release-on-request mode.
release-when-done mode. When this bit is low, the
requester operates in the release-on-request mode.
LVFAIR
When this bit is high, the requester operates in the fair
mode. When this bit is low, the requester does not operate
in the fair mode. In the fair mode, the requester waits until
the request signal line for the selected level is inactive
before requesting the VMEbus.
mode. When this bit is low, the requester does not operate
in the fair mode. In the fair mode, the requester waits until
the request signal line for the selected level is inactive
before requesting the VMEbus.
DWB
When this bit is high, the VMEchip2 requests the
VMEbus and does not release it. When this bit is low, the
VMEchip2 releases the VMEbus according to the release
mode programmed in the LVRWD bit. When the
VMEbus has been acquired, the DHB bit is set.
VMEbus and does not release it. When this bit is low, the
VMEchip2 releases the VMEbus according to the release
mode programmed in the LVRWD bit. When the
VMEbus has been acquired, the DHB bit is set.
ADR/SIZ
$FFF40030 (8 bits [7 used] OF 32)
BIT
15
14
13
12
11
10
9
8
NAME
ROBN
DHB
DWB
LVFAIR
LVRW
D
LVREQL
OPER
R/W
R
R/W
R/W
R/W
R/W
RESET
0 PS
0 PS
0 PSL
0 PS
0 PS
0 PS