diff --git a/main.cpp b/main.cpp
index 74d3ced..8227939 100644
--- a/main.cpp
+++ b/main.cpp
@@ -508,7 +508,8 @@ void print_help(const char* exe_name) {
         << "  di1_group_avg -> with tty + di1:trace, emit one averaged 4-word step per constant DI1 run\n"
         << "  do1_toggle_per_frame -> DI_SYN2 level-gated DO1 modulation:\n"
         << "                         DO1 is forced LOW when DI_SYN2 is LOW,\n"
-        << "                         while DI_SYN2 is HIGH DO1 toggles every 3 complete CH1+CH2 frames\n"
+        << "                         while DI_SYN2 is HIGH on the full frame (CH1 and CH2 ticks),\n"
+        << "                         DO1 toggles every 3 complete CH1+CH2 frames\n"
         << "  tty+di1_group_avg -> fast stream-only mode: skip CSV/SVG/live outputs and send only averaged tty data\n"
         << "  If sample_clock_hz is omitted together with clock:internal, the maximum ADC speed is used\n"
         << "\n"
@@ -1589,6 +1590,7 @@ int run(const Config& cfg) {
     bool do1_output_high = false;
     bool do1_gate_active = false;
     uint32_t do1_frames_since_toggle = 0;
+    bool do1_frame_all_high = true;
     uint64_t do1_packet_toggle_count = 0;
     uint64_t do1_packet_queued_words = 0;
     uint64_t do1_packet_sent_words_baseline = 0;
@@ -1793,6 +1795,7 @@ int run(const Config& cfg) {
         } else {
             do1_output_high = do1_high;
         }
+        flush_dout_queue(0U, false);
     };
 
     auto do1_on_packet_start = [&]() {
@@ -2222,8 +2225,10 @@ int run(const Config& cfg) {
             }
             const bool frame_complete = (lch == (cfg.channel_count - 1U));
             if (cfg.do1_toggle_per_frame) {
+                do1_frame_all_high = do1_frame_all_high && di_syn2_level;
                 if (frame_complete) {
-                    do1_on_frame_complete(di_syn2_level);
+                    do1_on_frame_complete(do1_frame_all_high);
+                    do1_frame_all_high = true;
                 }
             }