07 - Block reference

Every block, every pin. For what they are for, see
04 - Being a device and
05 - Reading and writing.

Eleven function blocks: three you will always use, five you will use often, and three you place only when a default is not what you want.

Every block but MODBUS_NODE and MODBUS_BRIDGE takes the node on a NODE
in-out pin and returns ERROR and STATUS. The pin must be assigned at
every call — leaving it out is a compile error.

MODBUS_BRIDGE stands alone and takes no node, because a bridge is not a
client or a server: it is both ends of a wire.

MODBUS_NODE

The link. Call it first, in a fast task of its own. Eleven pins are the whole
of an ordinary link — everything else lives on the three optional blocks
below, so it costs you nothing until you want it.

The prefix says which transport a pin belongs to, and a pin for a transport
you are not using is ignored. SERIAL_UNIT_ID is the one people expect to need
on TCP and do not.

The node waits one scan before opening, so a helper below may sit anywhere
in the same program — above or below. That is one millisecond of a fast task,
and it removes a placement rule nobody would remember.

MODBUS_CONFIG — optional

Tuning. Place it only where a default is not what you want.

Automatic recovery is already on and needs no block. A link that drops is
retried every two seconds until it returns, and every watched value is made due
the moment it does. RECONNECT only paces that differently, or turns it off.

Assign TIMEOUT even when you want the default. It is the first pin, and
the editor reports a block whose first input is never assigned. TIMEOUT := 0
says "I have thought about the timeout and I want the measured one", which is
worth saying on a tuning block.

MODBUS_IDENTITY — optional

What this node answers function code 43 with.

Worth setting on anything somebody else will commission: six identical-looking
nodes on one segment are six nodes you can only tell apart by asking.

MODBUS_ARDUINO — optional, boards only

The pins only a board has. On the Runtime it reports
MODBUS_INVALID_ARGUMENT rather than doing nothing quietly.

MODBUS_MAP

Your variables at Modbus addresses. No request pin: once bound, the variable
is the register.

MODBUS_READ

Reads a device, on a rising edge of REQ.

MODBUS_WRITE

Writes a device, on a rising edge of REQ.

MODBUS_WATCH

A repeating read, with a quality. Never touches the wire itself.

A new UNIT, FC, ADDRESS or ORDER re-aims the same watch: QUALITY goes
back to UNKNOWN and the next read goes to the new place.

MODBUS_POINT

One value on a device, defined entirely by settings: read and re-read from its
pins every scan. See 11 - Points from settings.

MODBUS_POINTS

The same, as a table: one block for every point on the bus.

MODBUS_PT_CFG (settings): unit, fc, address, dtype, order, bit,
scale (1.0), offset, every (T#1s), stale, timeout, enable (TRUE).

MODBUS_PT_STS: w (your logic: the value to write), and the status v, q,
ok, quality, age, failures, result.

MODBUS_STATUS

How the link is doing. No inputs: it reports and changes nothing.

MODBUS_DEVICE

How one device is doing. Free while POLL is 0 — it reads the traffic your
program already makes and sends nothing. Which means a device nobody asks
anything reads as not answering: give POLL to a device this block is the
only thing pointed at.

MODBUS_BRIDGE

TCP clients in front, a serial segment behind. Takes no NODE; put it in the
fast task a node would go in.

The enumerations

Not in this version

FC 23, read/write multiple registers. It needs a second buffer and a second
address, which would leave four pins dead on every ordinary write. Use a write
followed by a read.

FC 43 as a general call. It appears as the identity outputs on
MODBUS_DEVICE instead, which is what anybody actually wants from it.

Next: 08 - Patterns