Moxa UC-7101

Moxa · DIN-rail embedded computer · UC-7101

what it is

A palm-sized embedded computer for DIN-rail mounting: one serial port and one network port. Metal housing, 67 × 100.4 mm with a thickness of 22 mm, weighing just 130 g. DC power 12–48 V through a three-pin terminal block, draw up to 4.5 W.

The difference from a serial device server is fundamental. A device server passes bytes along unchanged. This device has its own operating system — uClinux on an ARM9 192 MHz processor with 16 MB of memory — so it can filter, convert or buffer data before it goes out to the network. It is useful where the raw stream from a device is too dense or in the wrong format.

It is managed over telnet and FTP. This system image has no SSH at all, and the web server shows only a factory test page — it is not a management panel.

The serial port is software-switchable between RS-232, RS-422 and RS-485, so a single device can handle three different cabling standards without changing hardware.

There is also an SD card slot, but on the side wall, under a cover — the manufacturer describes it as internal, accessible after removing the cover. The console port is also internal: the kit includes an adapter from the internal connector to DB9.

It neither accepts nor supplies PoE. The datasheet lists a single power input and the three-pin terminal block as the only power connector.

Watch out for the siblings and for the manufacturer datasheet. The same series includes the UC-7110 and UC-7112 — two serial ports and two network ports instead of one and one. The current datasheet gives a height of 26 mm for the UC-7101, but this number was copied from the siblings: an older datasheet from the same manufacturer, a measurement of the drawing in two independent editions and a check on the UC-7110 model consistently indicate 22 mm.

what we read from it

• The number of serial ports and how many of them are in use. A serial port has no "link" in the networking sense, so this is the only information on whether anyone is using it.
• Firmware version and the system name set on the device.
• Uptime since power-on. For a computer sitting between the network and a machine, a restart is sometimes the only trace of a power loss on the machine side — and for a device with its own system, also a trace that something inside it crashed.
• The full set of network link data: negotiated speed, duplex, medium, the port number on the switch, transmit and receive error counters with the per-minute increase, the number of link drops, spanning tree changes and a link quality rating.
• Transmitted and received traffic.
• Serial port settings — speed, data bits, parity and stop bits from the standard RS-232 table.
• Availability and response latency.

port layout

The drawing shows both faces. On the front there is a single male DB9 connector, offset slightly to the left of center, with screw standoffs on both sides. The manufacturer labels it on the housing "RS-232/422/485 P1".

On the rear face, from the left: a three-pin terminal block (the only power input), a reset hole pressed with a pin, and the network port. There is no barrel jack — and this is a visible difference from the serial device server of the same brand, which has two independent power inputs.

The network port has no number on the housing.

The number of status LEDs in the manufacturer datasheet is inconsistent — four on the dimensional drawing, three on the illustration — and the drawing does not give their positions.

what to watch out for

• SNMP responds only in version 1. A v2c query ends in a timeout, which is easy to mistake for SNMP being absent.
• The firmware version is only in the system description — the manufacturer branch in SNMP is empty.
• The factory system name is the manufacturer's website address (moxa.com.tw), and the device identifies itself with it in SNMP and in FTP. A new name takes effect in SNMP only after a restart.
• The clock has no battery backup. After every boot the system comes up with the date January 1, 2000; the time has to be set from an NTP server at startup.
• The file system is almost entirely read-only. The writable directories share a single 3.25 MB partition, and /var is a RAM disk that disappears on restart.
• FTP does not set execute permissions. An uploaded script exists but does not run — permissions have to be granted over telnet.
• The system shows a second network interface with a MAC address made up entirely of "FF". It is a leftover from the dual-port sibling, not a second port.
• The grep tool does not know the -E option (BusyBox 1.00) — scripts from other systems can break on this.

what we cannot read

• What is connected to the serial port, or whether it responds.
• Which standard the port runs in — RS-232, RS-422 or RS-485. This is switched by a command in the device's system, and SNMP does not report it.
• Processor load, memory or temperature over SNMP — even though it is a computer with its own system. They can be read only from inside the system.

full parameter list

A full parameter list for this model is not here yet — the ones described above are those we have read and verified. A missing list does not mean the device exposes nothing more.