constraints comments about DAC output strength for earphones

pull/3/head
emard 6 years ago
parent c6467c8c5b
commit daa7300fda

@ -138,8 +138,9 @@ IOBUF PORT "adc_sclk" PULLMODE=UP IO_TYPE=LVCMOS33 DRIVE=4;
# 4-bit mode can drive down to 75 ohm load impedance.
# Lower impedance leads to IO overload,
# FPGA will stop working and need reboot.
# For standard 17 ohm earphones:
# For standard 16 ohm earphones on PCB v1.7:
# use bits 2,3 as input (High-Z) and drive only bits 0,1.
# PCB v2.1.2 and higher can use full 4 bits and 16 mA drive for 16 ohm earphones.
LOCATE COMP "audio_l[3]" SITE "B3"; # JACK TIP (left audio)
LOCATE COMP "audio_l[2]" SITE "C3";
LOCATE COMP "audio_l[1]" SITE "D3";

@ -138,12 +138,8 @@ IOBUF PORT "adc_miso" PULLMODE=UP IO_TYPE=LVCMOS33 DRIVE=4;
IOBUF PORT "adc_sclk" PULLMODE=UP IO_TYPE=LVCMOS33 DRIVE=4;
## Audio 4-bit DAC "analog", "gpio" sheet
# 4-bit mode can drive down to 75 ohm load impedance.
# Lower impedance leads to IO overload,
# FPGA will stop working and need reboot.
# For standard 17 ohm earphones on PCB v1.7:
# use bits 2,3 as input (High-Z) and drive only bits 0,1.
# PCB v2.1.2 can use full 4 bits and 16mA drive for 17 ohm earphones.
# Output impedance 75 ohm.
# Strong enough to drive 16 ohm earphones.
LOCATE COMP "audio_l[3]" SITE "B3"; # JACK TIP (left audio)
LOCATE COMP "audio_l[2]" SITE "C3";
LOCATE COMP "audio_l[1]" SITE "D3";

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