HMS AnyBus DataTransfer Design Manual page 21

POLL mode
The following flow chart shows the necessary procedure for accessing the DPRAM in poll mode.
START
APP_IND = 02
(3FEh)
WAIT 0.1 ms
AB_IND
=
0F
No
AB_IND
=
F2
No
Yes
ACCESS
DPRAM
APP_IND = 01
WAIT 0.1 ms
AB_IND
=
FF
No
AB_IND
=
01
No
Yes
STOP
Figure 6. Poll mode
Yes
Yes
HMS F
IELDBUS
DPRAM accessing
in POLL mode
request control
over DPRAM
ERROR encountered?
then retry
request OK?
read output data,clear
new data flag (3fd);
write input data;
access time max. 1 sec.
request release
the DPRAM
ERROR encountered;
retry release
release OK?
DPRAM accessing
completed
S AB
YSTEMS
Design Guide
Revision 1.12
1998-08-12
Page 21 (35)