diff --git a/F1:F103/FX3U/Readme.md b/F1:F103/FX3U/Readme.md
index 3255ae4..614323e 100644
--- a/F1:F103/FX3U/Readme.md
+++ b/F1:F103/FX3U/Readme.md
@@ -426,7 +426,7 @@ Errors: `02` — bad start channel; `03` — bad amount (zero or beyond last cha
 #### 05 — write coil
 Changes a single relay state. `regaddr` — relay number, `nregs` — value (0 = off, non-zero = on).
 
-Example:
+Example - turn on coil 3:
 - request: `01 05 00 03 00 01`
 - answer: `01 05 00 03 00 01`
 
@@ -446,9 +446,13 @@ Changes all relays at once. `regaddr` must be 0, `nregs` a multiple of 8, `N` =
 Each data bit is a relay state.
 
 Example — turn on relays 0..7:
-- request: `01 0f 00 00 00 08 ff 01`
+- request: `01 0f 00 00 00 08 01 ff`
 - answer: `01 0f 00 00 00 08`
 
+Turn on all relays (0..7 and 10, 11):
+- request: `01 0f 00 00 00 10 02 ff 0f`
+- answer: `01 0f 00 00 00 10 56 c2`
+
 Errors: `02` — non-zero `regaddr`; `03` — wrong amount; `07` — cannot change relays.
 
 #### 10 — write multiple registers
diff --git a/F1:F103/FX3U/fx3u.bin b/F1:F103/FX3U/fx3u.bin
index 55efcb6..61f8bd0 100755
Binary files a/F1:F103/FX3U/fx3u.bin and b/F1:F103/FX3U/fx3u.bin differ
diff --git a/F1:F103/FX3U/fx3u.creator.user b/F1:F103/FX3U/fx3u.creator.user
index d15f67a..a7a0aee 100644
--- a/F1:F103/FX3U/fx3u.creator.user
+++ b/F1:F103/FX3U/fx3u.creator.user
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE QtCreatorProject>
-<!-- Written by QtCreator 20.0.2, 2026-10-01T16:22:16. -->
+<!-- Written by QtCreator 20.0.2, 2026-10-01T17:35:26. -->
 <qtcreator>
  <data>
   <variable>EnvironmentId</variable>
diff --git a/F1:F103/FX3U/modbusproto.c b/F1:F103/FX3U/modbusproto.c
index 3496fcb..ea4bb5b 100644
--- a/F1:F103/FX3U/modbusproto.c
+++ b/F1:F103/FX3U/modbusproto.c
@@ -45,13 +45,12 @@ TRUE_INLINE void readcoil(modbus_request *r){
         return;
     }
     uint8_t bytes[OUTMAXBYTES] = {0};
-    int curidx = OUTMAXBYTES;
     int vals = get_relay(OUTMAX+1);
     for(int i = 0; i < amount; ++i){
         bytes[i] = vals & 0xff;
         vals >>= 8;
     }
-    modbus_response resp = {.Fcode = r->Fcode, .ID = the_conf.modbusID, .data = bytes+curidx, .datalen = amount};
+    modbus_response resp = {.Fcode = r->Fcode, .ID = the_conf.modbusID, .data = bytes, .datalen = amount};
     modbus_send_response(&resp);
 }
 
diff --git a/F1:F103/FX3U/version.inc b/F1:F103/FX3U/version.inc
index 033da29..da4a632 100644
--- a/F1:F103/FX3U/version.inc
+++ b/F1:F103/FX3U/version.inc
@@ -1,2 +1,2 @@
-#define BUILD_NUMBER "120"
+#define BUILD_NUMBER "121"
 #define BUILD_DATE "2026-10-01"