
Attenuation settings
The attenuation is set by the attenuation data in the first byte and the command in the byte that follows. The data
value can be in the range $00 to $EE (0 to 238).
Audio output = 20 log
[dB]
— Since the ATT DATA is set to 0 (a muting of –
∞) by a reset, to output the audio signal, the control
microprocessor must issue, for example, a $EE + $81 command, thus setting both the left and right channels to
–0.63 dB.
Note: To prevent noise due to arithmetic overflow in the 1-bit D/A converter, data values of $EF (ATT DATA
= 239) or larger are not allowed.
Mute output; Pin 46: MUTEL, pin 59: MUTER
These pins output a high level when the attenuator coefficient is set to $00 and the data in each channel has been
zero continuously for a certain period. If data input occurs once again, these pins go low immediately.
16. Digital filter outputs; Pin 34: LRCKO, pin 35: DFLRO, pin 36: DACKO
DFLRO outputs 2
× oversampled data for use with an external D/A converter MSB first in synchronization with the
falling edge of DACKO. These pins are provided so that an external D/A converter can be used if desired.
17. Swap; Pin 48: LCHP, pin 49: LCHN, pin 56: RCHN, pin 57: RCHP
The swap command swaps the D/A converter left and right channel outputs.
18. One-bit D/A converter
The LC78630E PWM block outputs one data value in the range –3 to +3 once every 64fs period. To reduce carrier
noise, this block adopts an output format in which the output is adjusted so that the PWM output level does not
invert between consecutive data items. Also, the attenuator block detects 0 data and enters muting mode so that
only a 0 value (a 50% duty signal) is output.
This block outputs a positive phase signal to the LCHP (RCHP) pin and a negative phase signal to the LCHN
(RCHN) pin. High-quality analog signals can be acquired by taking the differences of these two output pairs using
external low-pass filters.
The LC78630E includes built-in radiation suppression resistors (1 k
) in each of the LCHP/N and RCHP/N pins.
ATT DATA
256
No. 5121-22/33
LC78630E
Code
Command
RES = low
$85
SWAP ON
$84
SWAP OFF
q