BU8871F Rohm, BU8871F Datasheet - Page 9

• Manufacturer Part Number: BU8871F
• Description: DTMF receiver for telephones
• Manufacturer: Rohm

(4) ESt output
The ESt guard time is determined by the CPU of the host
computer, but to reduce the load on the host computer,
the guard time can be set using an external circuit, as
shown below.
The relation between a momentary falter in the ESt guard
time (t.
(t
shows a timing diagram for guard times.
FOperation notes
Oscillation frequency precision can be a problem with ce-
ramic resonators. Before including a ceramic resonator
in your design, please consult the resonator manufactur-
er to make sure this will not be a problem.
188
S Oscillation
Communication ICs
GH
), and the time constant is shown below. Figure 10
GL
), a momentary HIGH level in the ESt guard time
Also, if an external clock is being injected, a DC blocking
capacitor must be inserted. Select a capacitor that will
neither attenuate the frequency components or put an
excessive load on the drive side.
BU8871F