From d3d5848a5f6d0a4d55f194972a158795c286d818 Mon Sep 17 00:00:00 2001
From: Yuuta Liang <yuuta@yuuta.moe>
Date: Thu, 9 Nov 2023 09:16:31 +0800
Subject: AP7921

---
 docs/sysadmin/misc/ap7921.md | 52 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/docs/sysadmin/misc/ap7921.md b/docs/sysadmin/misc/ap7921.md
index a68f138..4ecf6a0 100644
--- a/docs/sysadmin/misc/ap7921.md
+++ b/docs/sysadmin/misc/ap7921.md
@@ -1 +1,53 @@
 # APC AP7921
+
+AP7921 is a 1U 8-outlets switched PDU from APC.
+
+* No per-out metering.
+* Outlet is C14; Input is C20.
+* Although spec says 220V input, 110V also works.
+* AVR control plane.
+* Only supports old cipher like 3DES.
+* The meter precision is lower than AP7921B.
+* The console is menu-based and is pretty hard to use (AP7921B is console-based).
+
+## Console Cable
+
+AP7921 has a reset button, but it only allows temporary logon to the serial
+console via default username and password (`apc` / `apc`). It won't reset web
+portal password. Thus, you have to get a console cable if you loss the password.
+
+Even worse, APC uses the wired RJ12 connector for console rather than RS232 or
+RJ45. Instead of buying a cable, I highly recommend you to make your own.
+
+Ingredients:
+
+* RJ12 male connector: Must be 4pin / 6pin. 2pin RJ11 won't work.
+* RS232 female connector
+
+Wiring:
+
+```
+  RS232 F      RJ12 M
+                ┌──┐
+┌─────────┐    ┌┴──┴┐
+│5 4 3 2 1│  ┌─┘    └─┐
+└┐9 8 7 6┌┘  │ 654321 │
+ └───────┘   └────────┘
+Female 5GND     Male
+     Front  Facing
+ GND 5──────────5
+  TX 2───────────4
+  RX 3────────────3
+ GND 5─────────────2
+```
+
+Taken from
+[pinoutguide.com/UPS/apc_940-0144a_cable_pinout.shtml](https://pinoutguide.com/UPS/apc_940-0144a_cable_pinout.shtml)
+but swapped RX and TX.
+
+Serial parameters:
+
+* Baud rate: 9600
+* No stop bit
+
+You need to press enter several times for the login prompt to show up.
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