Sundance SMT335E - Manual (Page 34)

Version 1.5 Page 34 of 53 SMT335E SMT375E User Manual
Programmable Wait States
The SMT335E has its own internal software-configurable wait-state generator that is
used in conjunction with the external ready line, RDY. You control the generator by
configuring two fields in the Global Bus Control Register: WTCNT specifies the
number of software wait states to generate and SWW selects one of four options.
RDY
wtcnt
is an internally generated ready signal. When an external access is begun,
the value WTCNT is loaded into a counter; WTCNT can be any value from 0 through
15. The counter is decremented every H1/H3 clock cycle until it becomes 0. Once the
counter reaches 0, it will remain at 0 until the next external access. RDY
wtcnt
will be 1
while the counter is nonzero and 0 otherwise.
The four SWW options combine RDY and RDY
wtcnt
to generate the internal ready
signal, RDY
int
that controls accesses. As long as RDY
int
= 1, the current external
access is extended. When RDY
int
becomes 0, the current access will complete.
SWW = 00
2
RDY
int
= RDY; RDY
wtcnt
is ignored.
SWW = 01
2
RDY
int
= RDY
wtcnt
; RDY is ignored.
SWW = 10
2
RDY
int
= RDY
wtcnt
OR RDY; either generates ready.
SWW = 11
2
RDY
int
= RDY
wtcnt
AND RDY; both must occur to generate ready.
Additional information is available in the TMS320C4x User’s Guide [5] chapter 9.4:
Programmable Wait States.
Note that bus sharing is supported in firmware versions 2.5 and above. The global
bus lines will be tri-stated according to the state of the AE, DE and CE lines.