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
C-Boot ROM Description
613
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
ROM Code and Peripheral Booting
Figure 6-31. 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
, discards the upper 8 bits of the first read from the port and
treats the lower 8 bits masked with GPIO9 in bit position 7 and GPIO8 in bit position 6 as the the least
significant byte (LSB) of the word to be fetched. The routine will then perform a second read to fetch
the most significant byte (MSB). 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.