IP2022 User’s Manual—In-System Debugging www.ubicom.com 347 Figure 5-6  Serial Debug Unit After  sending  a  command,  the  debugger/programmer  has  to
check that the command has completed before sending another
command. There are several ways to do this: • Allow sufficient time to elapse before sending another com-
mand. • Issue a NOP command, and check the DONE bit in the com-
mand acknowledge frame. • Poll the TSO signal, waiting for it to be sampled high. When
the processor completes the requested command, the com-
mand byte with its most-significant bit (i.e. the DONE bit) set
is loaded into the SPI shift register, which causes the TSO sig-
nal to be driven high. To make the state of the DONE bit visible
on the TSO signal, the select line TSS must be asserted.  Personal
Computer Printer Port   or
USB  Serial
Debug Unit 515-057.eps Cable Target
System