®
PMD-100
PMD-100 Process Decoder
Attenuation Mode
In Program mode, the PMD-100 has a digital attenuator which can be set for each channel in increments of 0.188 dB
between 0 and approximately 96 dB of attenuation. The attenuation value is entered MSB first as a 9 bit word on the
MDT pin. The same value attenuation may be clocked to both left and right registers by the use of the attenuators mode
controls (see timing diagram below). Changes in attenuation value are always carried out smoothly at a rate of one 0.188
dB step every 16 input samples. The delay between an attenuation command and the first sample it affects can be
between 84 and 100 input samples.
Since the PMD-100 has no reset pin, when it is powered up in Program mode, the attenuator registers will contain
arbitrary values. As part of the initial programming, it is necessary to issue a ZERO attenuation command or set the
attenuation to known value using the SET LEFT and SET RIGHT commands.
Attenuation Data Byte
Attenuation
Attenuation Data Byte
Attenuation
0 0000 0000
0 0000 0001
0 0000 0110
0 0000 1011
0 0001 0000
0 dB
0 0010 0000
0 0011 0101
0 0100 0000
0 1000 0000
1 0000 0000
1 1111 1111
6.016 dB
9.964 dB
12.032 dB
24.064 dB
48.128 dB
96.068dBs
0.188 dB
1.128 dB
2.068 dB
3.008 dB
Attenuation Register
Muting
The chip has two muting functions, hard mute and soft mute, which are activated by raising the respective input pins
HMUTE and SMUTE to logic high. The soft mute ramps the output signal down at the same rate as the digital
attenuator (one step per 16 input samples). It is designed for voluntary muting, such as when changing input selection.
The hard mute goes to full attenuation in approximately 1millisecond, which is less than the group delay through the
filter, and is intended to be used for emergency situations such as loss of input signal. Both muting functions release
softly, at the rate of the digital attenuator. When combined with the fact that the chip continues to supply clock signals
to the DAC’s in the absence of input signals, the digital muting may eliminate the need for analog muting in many circuit
designs. Note that during soft mute, the output dither remains on, while during hard mute, output dither is off.
Pacific Microsonics, Inc.
13
32990 Alvarado Niles Road, Suite 910
Union City, CA 94587
Phone (510) 475-8000
Fax (510) 475-8005
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