Tags, internal memory and the command block in PM Designer

Internal memory: $U, $N, $S, $I

The panel's own memory is addressed with a dollar sign and a letter (Section 3.3.1). A word is $U100; a bit inside it is $U100.5, with the bit number in hexadecimal 0 to f.

Set the size of $U and $N in the Internal Memory dialog under the Links node (Section 3.3.4). Keep $N as small as the job needs: battery-backed RAM is shared with recipe blocks, alarm logging and data loggers, and the compiler tells you when it runs out.

System words you will actually use

• $S46 to $S53: second, minute, hour, tenth of a second, day (0 = first), month (0 = January), year (0 to 99) and day of week (0 = Sunday) as binary values. $S42 to $S45 hold the same clock in BCD.
• $S219: the current user level, 0 to 9, where 9 means the developer password was used. Compare it in a macro to lock operations.
• $S0 to $S25: the keypad input buffer, used by custom keypads.
• $S1039 (V4): write a time-zone code here to change the panel's time zone at runtime (Chapter 12).

Index registers and indirect addressing

Put an index register inside square brackets and the address is computed at runtime (Section 3.3.2): W[$I30] is W2000 when $I30 holds 2000; $U[$I0+123] is $U223 when $I0 is 100; [$I2]:W100 addresses word 100 on the sub-link node held in $I2 (only $I0 to $I15 may be used for the node, without offset). One screen of "station n" objects can therefore show any station by changing $I2 in a macro or a word button. The software cannot check that the computed address exists, so bound the index yourself. Index registers are battery backed where the panel has that memory and are cleared when the application is updated.

PLC addresses

An address on a link uses the device's own notation: D100, MW70, 40001, DB10.DBW20. Without a prefix it refers to link 1; 2\D100 is D100 on link 2; 3:W100 is word 100 on sub-link node 3; 2\3:W100 combines both. The Address Input Keypad, opened by the small keypad icon next to any address field, lists only the register types the chosen driver supports, which is the quickest way to learn a driver's syntax. The manual explains the terms Write Address, Monitor Address, Read Address and Notification Bit in Section 4.4.3.1; the pattern is that buttons write, lamps monitor, displays read, and a notification bit lets the panel tell the PLC an operation finished.

Tags

A tag is a name for an address with a data type and a scan rate (Section 2.3). Use tags from the first day: an object bound to 1\MOTOR\Run_Cmd keeps working when the PLC address behind it changes, and the tag list doubles as the interface document between HMI and PLC programmer. The tags editor (Panel > Tags for local tags, Project > Global Tags for global ones) has a Tag Group Explorer on the left, where links, recipes and data loggers each own groups and sub-groups, and a tag list on the right with Name, Alias For, Data Type, Address, Scan Rate and Description columns.

• Local tags belong to one panel application; global tags are shared by every application in the project, must start with an underscore (_ALARM_SHOW) and can only point at internal memory.
• Array tags name a contiguous block: TANK[5] is the sixth element of a one-dimensional array, FLAG[1,2] and _Temp[1,0,2] address two- and three-dimensional ones. The element number is row times columns plus column, as the manual's examples show.
• Structure tags hold several members of different types under one name: Valve_1.Position. Structures are defined on the Data Type tab with continuous or random addressing and word or double-word alignment, and can be imported from a CSV.
• Aliases let one address carry several names; the settings of an alias cannot differ from its tag.
• Names may be up to 48 characters, cannot start with a digit and cannot equal a macro keyword. Scan Rate is Fast or Normal; give Fast only to the handful of tags a screen must refresh quickly.

Tags import and export as tab-delimited CSV (right-click a link or group, Preview/Import Tags or Export Group), which is how a PLC symbol table becomes an HMI tag list in minutes. For Beckhoff, Allen-Bradley, CoDeSys, Mitsubishi, Omron EtherNet/IP and Panasonic controllers PM Designer can read the controller's own tag data types, and the OPC UA driver loads tags straight from the server.

The command block and status words

The command block is a block of words, in the PLC or in internal memory, that the panel scans every 0.25, 0.5 or 1 second and obeys (Section 3.6). The status words are words the panel writes back. Together they let the PLC program switch screens, change language, select a recipe, write a recipe to or from the PLC, clear the alarm history or counts, sound the buzzer, trigger event macros and save files, and let it know which screen, recipe, language and user level the panel is on. Open the Command & Status dialog from the Setup node of the panel application.

Type A is the choice for new projects. You tick only the words you need and the panel reads only those, in default or custom order: a Screen Switching Register, Parameter One to Three registers, a Command Flag Word with 16 flags, 32 trigger bits (each able to start an event macro or a data logger sample), 16 enabling bits and more. The status words report command flag acknowledgement, trigger acknowledgement, current screen number, current recipe block and number, current user level and current language. Type H packs screen number, language and backlight control into one word with fixed bit assignments and offers a binary or BCD flavour; it exists for compatibility with older projects.

Flag 15 of the Type A command word issues a general command (Section 3.6.7): put an operation code in Parameter One and a data ID in Parameter Two, raise the flag, and the panel saves logged data, alarms, counts, recipes or a screen print to a file with a default name such as DL3_date_time.csv. It is the simplest way to make the PLC archive data on a shift change without a macro.

Data types and display formats

Whatever the source, each object states how to interpret the word or words it reads: 16- or 32-bit signed or unsigned integer, 16- or 32-bit BCD, 32-bit floating point, byte array (ASCII string) or word array (double-byte string). Numeric objects add a display type (decimal, hexadecimal, octal, exponential, IP address) and scaling, so a 0 to 27648 analogue input can be shown as 0.0 to 100.0 percent without a macro. Get the data type wrong and the value is garbage; a 32-bit float read as a 16-bit integer is the classic case. Match the PLC programmer's declaration, and remember that a 32-bit value occupies two consecutive words.