Rainbow Electronics U3742BM - Manual (Page 22)

22
U3742BM
4735A–RKE–11/03
Table 10. Effect of the Configuration Word Lim_max
Conservation of the Register
Information The U3742BM has an integrated power-on reset (POR) and brown-out detection cir-
cuitry to provide a mechanism to preserve the RAM register information.
According to Figure 23, a power-on reset is generated if the supply voltage V
S
drops
below the threshold voltage V
ThReset
. The default parameters are programmed into the
configuration registers in that condition. Once V
S
exceeds V
ThReset
, the POR is canceled
after the minimum reset period t
Rst
. A POR is also generated when the supply voltage of
the receiver is turned on.
To indicate that condition, the receiver displays a reset marker (RM) at pin DATA after a
reset. The RM is represented by the fixed frequency f
RM
at a 50% duty cycle. RM can be
canceled via an 'L' pulse t
1
at pin DATA. The RM implies the following characteristics:
• f
RM
is lower than the lowest feasible frequency of a data signal. This means, RM
cannot be misinterpreted by the connected microcontroller.
• If the receiver is set back to polling mode via pin DATA, RM cannot be cancelled by
accident if t
1
is applied according to the proposal in the section “Programming the
Configuration Register” on page 23.
By means of that mechanism, the receiver cannot lose its register information without
communicating that condition via the reset marker RM.
Figure 23. Generation of the Power-on Reset
Lim_max Upper Limit Value for Bit Check
Lim_max < 12 is not applicable (T
Lim_max
= (Lim_max - 1) × XLim × T
Clk
)
0 0 1 1 0 0 12
0 0 1 1 0 1 13
0 0 1 1 1 0 14
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
0 1 1 0 0 0
24 (Default)
(USA: T
Lim_max
= 375 µs, Europe: T
Lim_max
= 381 µs)
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1 1 1 1 0 1 61
1 1 1 1 1 0 62
1 1 1 1 1 1 63
V
S
POR
DATA (U3742BM) X
1/f
RM
t
Rst
V
ThReset