Start transfer
No
More
data
?
Device ready
(GPIO26=0)
?
Yes
Load GPIO[9,8,5:0] with data
Signal that data
is ready
(AIO12=0)
Device ack
(GPIO26=1)
?
No
Yes
Acknowledge device
(GPIO27=1)
Yes
No
End transfer
M-Boot ROM Description
567
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
ROM Code and Peripheral Booting
Figure 6-8. Parallel GPIO Mode - Host Transfer Flow
shows the flow used to read a single word of data from the parallel port.
•
8-bit data stream
The 8-bit routine, shown in
, shows how the least significant byte (LSB) of the word is to be
fetched. The routine will then perform a second read to fetch the most significant byte (MSB). It then
combines the MSB and LSB into a single 16-bit value to be passed back to the calling routine.