This article explains which parameters a VMPS dispenser system requires for a connection to a bessa product. bessa implements VMPS according to version 5.16 (2015-07-03).
VMPS is the POS protocol of the Gruber dispenser systems and is also used by a number of compatible units. It is the only one of the three supported protocols that can run both serially over USB and over the network.
Prerequisites
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The POS interface is enabled on the dispenser and set to VMPS.
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For a serial connection: a USB-to-serial adapter between the device and the dispenser, plus the transmission parameters specified by the dispenser technician.
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For a network connection: the dispenser has a static IP in the local network or a reserved DHCP lease, and is reachable from the device.
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A dispenser profile exists in the bessa Manager, populated with article PLUs, user numbers and — if needed — table numbers. See Dispensers.
Where the parameters are entered
VMPS runs on either the Serial (USB) or the Network connection type; depending on that choice, one of the two parameter tables below applies. The values are entered in the respective bessa product — on the Sales Point under Dispenser Settings.
Parameters for a serial connection
For Serial (USB), the USB-to-serial adapter in use is selected and the four transmission parameters are entered. They must match the setting on the dispenser exactly.
|
Field |
Meaning |
Allowed values |
Typical value |
|---|---|---|---|
|
Baud rate |
Transmission speed in bit/s |
Integer, e.g. |
|
|
Data bits |
Number of data bits per character |
|
|
|
Stop bits |
Number of stop bits |
|
|
|
Parity |
Parity check |
|
|
Parameters for a network connection
For Network, communication runs over UDP.
|
Field |
Meaning |
Typical value |
|---|---|---|
|
IP address |
Static IP of the dispenser in the Sales Point network |
e.g. |
|
Port |
UDP port of the POS interface on the dispenser |
|
The dispenser driver occupies the same UDP port locally that it addresses on the dispenser. If several dispensers are connected over VMPS on the network, each unit must therefore use its own port — otherwise only the dispenser connected first can be addressed.
UDP is a connectionless protocol without delivery guarantees. The device and the dispenser have to sit in the same stable network segment. Wi-Fi links with roaming or packet loss lead to sporadically failing bookings. A wired connection is the more reliable option.
No digit settings required
Unlike the E protocol, VMPS defines its field widths in the specification. The dispenser driver applies them automatically — the configuration screen therefore shows neither digit settings nor a checksum switch.
|
Protocol field |
Fixed number of digits |
|---|---|
|
Waiter / user |
3 |
|
Table |
4 |
|
Product (PLU) |
4 |
|
Quantity |
5 |
|
Station |
2 |
|
Sequence number |
2 |
The XOR checksum is an integral part of every VMPS command and is always active. The dispenser driver also maintains a sequence number per dispenser that survives restarts and keeps commands and responses matched up.
Without an assigned user number: If no dispenser user number is stored for the booking user in the dispenser profile, waiter number 999 is transmitted over VMPS. The booking is carried out, but it is not attributed to a specific employee.
FAQ
Serial or network — which is better? The serial connection is the more robust option because it needs no network infrastructure, but it ties the device and the dispenser together physically. The network connection allows any distance, but requires a stable LAN and static addressing.
Which units speak VMPS? Gruber dispenser systems as well as compatible units and dispensers from other manufacturers. Ask the manufacturer or dispenser technician whether a specific unit supports VMPS and in which version.
Does the dispenser have to answer PING? No, but it helps with troubleshooting. If the unit does not answer ICMP, check the reachability of the configured UDP port instead.
Troubleshooting
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The connection test fails on a network connection — the IP or port is wrong, the dispenser sits in a different VLAN, or a firewall blocks UDP on the path to the dispenser.
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Only the first of several dispensers is reachable — several units use the same port. Assign each unit its own port.
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The connection test fails on a serial connection — baud rate, data bits, stop bits or parity do not match, or the USB adapter was not detected and the permission for it was not granted.
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Bookings arrive irregularly — a typical symptom of UDP over an unstable Wi-Fi link.
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Bookings are not attributed to any employee — the user numbers are missing in the dispenser profile, so
999is sent instead.
Related topics
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Dispenser Systems — overview of the supported protocols
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Dispenser Settings — connecting a dispenser on the Sales Point
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Dispensers — articles, users, tables and operating mode in the bessa Manager
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E Protocol Dispenser — serial alternative
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Network security & port requirements