From 1eb1675ec3b1f0df47a0a2a657f40e1fe8079693 Mon Sep 17 00:00:00 2001
From: Sarah Chen <schen@galionsystems.com>
Date: Fri, 28 Aug 2026 19:28:13 -0500
Subject: [PATCH] add write_coil for pump control commands

---
 galion_modbus/poll.py | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/galion_modbus/poll.py b/galion_modbus/poll.py
index 7a73f23..88f3010 100644
--- a/galion_modbus/poll.py
+++ b/galion_modbus/poll.py
@@ -31,3 +31,14 @@ def poll_site(site_cfg):
                 tag = plc.get("tags", {}).get(str(i), f"{plc['host']}:r{i}")
                 results[tag] = val
     return results
+
+
+def write_coil(host, port=502, unit=1, address=0, value=True):
+    """Write single coil — used for pump enable/disable commands."""
+    c = ModbusTcpClient(host, port=port)
+    c.connect()
+    try:
+        rr = c.write_coil(address, value, unit)
+        return not rr.isError()
+    finally:
+        c.close()