MC145026•MC145027•MC145028•SC41343•SC41344 MOTOROLA
14
MC145027 AND MC145028 TIMING
To verify the MC145027 or MC145028 timing, check the
waveforms on C1 (Pin 7) and R2/C2 (Pin 10) as compared to
the incoming data waveform on D
in
(Pin 9).
The R–C decay seen on C1 discharges down to 1/3 V
DD
before being reset to V
DD
. This point of reset (labelled “DOS”
in Figure 15) is the point in time where the decision is made
whether the data seen on D
in
is a 1 or 0. DOS should not be
too close to the D
in
data edges or intermittent operation may
occur.
The other timing to be checked on the MC145027 and
MC145028 is on R2/C2 (see Figure 16). The R–C decay is
continually reset to V
DD
as data is being transmitted. Only
between words and after the end–of–transmission (EOT)
does R2/C2 decay significantly from V
DD
. R2/C2 can be used
to identify the internal end–of–word (EOW) timing edge which
is generated when R2/C2 decays to 2/3 V
DD
. The internal
EOT timing edge occurs when R2/C2 decays to 1/3 V
DD
.
When the waveform is being observed, the R–C decay
should go down between the 2/3 and 1/3 V
DD
levels, but not
too close to either level before data transmission on D
in
re-
sumes.
Verification of the timing described above should ensure a
good match between the MC145026 transmitter and the
MC145027 and MC145028 receivers.
V
DD
0 V
D
in
V
DD
2/3
1/3
0 V
C1
DOS DOS
Figure 15. R–C Decay on Pin 7 (C1)
V
DD
2/3
1/3
0 V
R2/C2
EOT
Figure 16. R–C Decay on Pin 10 (R2/C2)
EOW
