From daa7300fdab7724bd0f0a888107918600b10f6ce Mon Sep 17 00:00:00 2001 From: emard Date: Wed, 14 Nov 2018 15:33:12 +0100 Subject: [PATCH] constraints comments about DAC output strength for earphones --- doc/constraints/ulx3s_v17patch.lpf | 5 +++-- doc/constraints/ulx3s_v20.lpf | 8 ++------ 2 files changed, 5 insertions(+), 8 deletions(-) diff --git a/doc/constraints/ulx3s_v17patch.lpf b/doc/constraints/ulx3s_v17patch.lpf index 5d29865..79f969a 100644 --- a/doc/constraints/ulx3s_v17patch.lpf +++ b/doc/constraints/ulx3s_v17patch.lpf @@ -136,10 +136,11 @@ 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, +# 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"; diff --git a/doc/constraints/ulx3s_v20.lpf b/doc/constraints/ulx3s_v20.lpf index efb89c7..2513460 100644 --- a/doc/constraints/ulx3s_v20.lpf +++ b/doc/constraints/ulx3s_v20.lpf @@ -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";