Working documentation

This page is generated from the project's working notes. It records a real retrofit in progress, corrections included. Anything marked 🔴 or ⚠️ is unresolved or carries a caveat - read those before acting.

The Mesa cards — every terminal, from the manuals

7 September 2026. Read directly from 7i77uman.pdf, 7i84uman.pdf and 7i76euman.pdf, all three on Drive. Every table below was cross-checked against the PDF text layer by word coordinate, because these are multi-column pin tables that interleave badly under plain text extraction.

This page exists to be printed. It is the terminal-by-terminal reference that turns "the X analog command goes to the 7I77U" into "land this wire on TB5 terminal 4."

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🔴 Four things to check against the physical boards before wiring

🔴 7I77U Rev A: TB7 and TB8 silkscreen labels are SWAPPED	The manual's own errata. Wire from the tables on this page, not from the board print. Check the board revision first
⚠️ 7I77U TB2 voltage rating disagrees with itself	The TB2 terminal table says 8-32 V; the narrative and the specification table both say 5-28 V. Confirm before choosing a field supply. 24 V is inside both, so this does not bite us
⚠️ 7I76EU calls its 5 V power connector both P4 and P5	Same connector, two names in one paragraph. Check the silkscreen
⚠️ 7I76EU jumper names conflict	IP address selection is W13/W14 in one section and W2/W3 in another; secondary flash is W7 in one place and W9 in another. Both look like manual typos. Confirm against the board before moving a jumper

✅ Pin 1 is marked with a square pad on the 7I77U and 7I76EU. On all three cards, pin 1 of a 24-way field block is at the bottom edge; on the 8-way power blocks pin 1 is the bottom pin and pin 8 the top.

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7I77U — analog servo interface

Connectors

	Type	Ways	For
P1	DB25F	25	Host interface to the 7I76EU
TB1	screw	2	Aux 5 V for the analog / encoder / RS-422 section
TB2	screw	8	Field power
TB3	screw	24	🔴 Encoders 0-2
TB4	screw	24	Encoders 3-5
TB5	screw	24	🔴 Analog drive interface — command and enable
TB6	screw	8	RS-422
TB7	screw	24	Field I/O — inputs 16-31, outputs 8-15
TB8	screw	24	Field I/O — inputs 0-15, outputs 0-7

🔴 TB5 — the analog drive interface

Four terminals per axis, and the enable sits alongside the command. This is the block the three servo drives land on.

Pin	Signal		Pin	Signal		Pin	Signal
1	ENA0-		9	ENA2-		17	ENA4-
2	ENA0+		10	ENA2+		18	ENA4+
3	GND		11	GND		19	GND
4	AOUT0		12	AOUT2		20	AOUT4
5	ENA1-		13	ENA3-		21	ENA5-
6	ENA1+		14	ENA3+		22	AOUT5 region
7	GND		15	GND		23	ENA5+
8	AOUT1		16	AOUT3		24	AOUT5

(Channels 4 and 5 follow the same 4-pin pattern; only 0-3 are used here.)

🔴 The enables are differential pairs (ENA+ / ENA-), not open-drain to ground. That is not the same shape as the SGDH's /S-ON, which is a sinking input against +24V-IN. How the two meet is a design question, not a wiring one — see servo-drive-interface.md.

⚠️ Analog wiring, from the manual: minimum load 2 kΩ; use shielded twisted pair with AOUTn to the drive's AIN+ and the adjacent GND to AIN-; tie the shield at the 7I77U end only; run the drive's common back to 7I77U power ground on a separate wire.

🔴 TB3 — encoders 0-2

Eight terminals per channel. +5V and GND are supplied by the card, so the encoder is powered from here.

Pin	Ch 0		Pin	Ch 1		Pin	Ch 2
1	QA0		9	QA1		17	QA2
2	/QA0		10	/QA1		18	/QA2
3	GND		11	GND		19	GND
4	QB0		12	QB1		20	QB2
5	/QB0		13	/QB1		21	/QB2
6	+5V		14	+5V		22	+5V
7	IDX0		15	IDX1		23	IDX2
8	/IDX0		16	/IDX1		24	/IDX2

✅ Differential is the factory default on all six channels, which is what the SGDH's PG output is. Nothing to change.

✅ IDX is on the block whether or not it is used — so landing the index wire costs one terminal and enables HOME_USE_INDEX later (see the homing note in pre-strip-survey.md item 4).

TB4 carries channels 3-5 on the identical pattern.

TB2 — field power

Pin	Signal	Feeds
1, 2	VFIELDA	🔴 TB7 — its outputs, and its input thresholds
3, 4	VFIELDB	🔴 TB8 — its outputs, and its input thresholds
5	VIN	field I/O logic power
6, 7	NC
8	GROUND	common to VIN and both VFIELD

🔴 Both VFIELDA and VFIELDB must be supplied or the card reports a low-voltage fault and will not start. Even if only one I/O block is used.

TB8 and TB7 — field I/O

TB8 pin		TB7 pin
1-16	INPUT0-INPUT15	1-16	INPUT16-INPUT31
17-24	OUTPUT0-OUTPUT7	17-24	OUTPUT8-OUTPUT15

Inputs are sinking, ~11 kΩ, threshold 50 % of the field supply with 10 % hysteresis — on 24 V that is high above 14.4 V, low below 9.6 V. INPUT0-INPUT3 can also read analog, 8-bit.

Outputs are universal — sourcing, sinking or push-pull, selectable per output in software. 500 mA per output, 2.0 A per driver chip (each chip serves eight sequential outputs), short-circuit trip about 1.5 A. ✅ Built-in flyback clamps — no external diodes needed on inductive loads.

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7I84U — isolated remote field I/O

	Type	Ways	For
TB1	screw	8	Power
TB2	screw	24	Inputs 16-31, outputs 8-15
TB3	screw	24	Inputs 0-15, outputs 0-7
J1	RJ-45	8	RS-422 to the 7I76EU

TB1 — power

Pin	Signal	Feeds
1, 2	VFIELDB	🔴 TB2
3, 4	VFIELDA	🔴 TB3
5	VIN	logic power, 8-32 V
6, 7, 8	GROUND

⚠️ Note the ordering is the opposite way round to the 7I77U — on the 7I84U, VFIELDB is on pins 1-2 and feeds TB2; on the 7I77U, VFIELDA is on pins 1-2 and feeds TB7. Easy to get wrong when wiring both cards in one session.

TB3 and TB2 — field I/O

Same layout as the 7I77U's blocks: pins 1-16 the sixteen inputs, pins 17-24 the eight outputs.

Inputs sinking, 22 kΩ (twice the 7I77U's), same 50 % threshold. Outputs 5-28 V, sourcing / sinking / push-pull per point, 500 mA.

Status LEDs — worth knowing before the first power-up

CR2 yellow, upper left	VIN power
CR5 red, lower left	🔴 field I/O fault
CR6 green, lower left	field I/O activity
CR7 yellow, bottom left	RS-422 cable power

✅ CR2 and CR7 must both be lit in normal operation.

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7I76EU — the host card

	Type	Ways	For
RJ-45		8	Host Ethernet
P1, P3	IDC header	26	Expansion I/O
TB1	screw	8	Field power
TB2	screw	24	Step/dir 0-3
TB3	screw	24	Step/dir 4, encoder, RS-422, unregulated logic power in
TB4	screw	8	Spindle
TB5	screw	24	Inputs 16-31, outputs 8-15
TB6	screw	24	Inputs 0-15, outputs 0-7
P4	screw	2	5 V logic power

TB4 — the spindle connector

Pin	Signal
1	SPINDLE-
2	SPINDLE OUT
3	SPINDLE+
4	NC
5	SPINDLE ENA- / FWD-
6	SPINDLE ENA+ / FWD+
7	SPINDLE DIR- / REV-
8	SPINDLE DIR+ / REV+

⚠️ The analog output here needs an external reference supply on SPINDLE+ / SPINDLE-, 5-20 V, SPINDLE+ always the more positive. Output current 5 mA. The ENA and DIR outputs are isolated, up to 100 V open circuit, 50 mA.

TB1 — field power

Pin	Signal
1-4	VFIELD
5	VIN
6, 7, 8	GROUND

⚠️ No VFIELDA/VFIELDB split on this card — one rail feeds both TB5 and TB6. Different from the other two.

TB5 and TB6 — field I/O

Same 16-in / 8-out layout. TB6 inputs 0-3 double as analog inputs; TB5 inputs 16-19 double as MPG quadrature. Inputs sinking, 10 kΩ. Outputs 500 mA.

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Rules that apply to all three cards

🔴 VFIELD must connect directly to the DC source	No switches, breakers or relay contacts in that circuit. A fuse is acceptable
🔴 Field power ramp rate under 10 V/ms	Which is another way of saying the same thing — it cannot be switched with a mechanical contact
✅ No flyback diodes needed	All three cards' output drivers have built-in clamps
⚠️ Sinking outputs must not drive a load tied to a higher voltage than VFIELD	It back-powers the field rail through the load
✅ Frame ground	The 7I76EU has a 0.250" blade tab near the Ethernet jack. Earth it

I/O capacity against what the machine needs

Card	Inputs	Outputs
7I76EU	32	16
7I84U	32	16
7I77U	32	16
Available	96	48
Needed	41	41

✅ Inputs are comfortable. Outputs are not — 41 of 48, leaving seven spare. ✅ The three servo enables do not eat into that, because they live on the 7I77U's TB5 alongside the analog commands, not on a field output block.

Related

• mesa-wiring-schedule.md — the signal-by-signal plan
• mesa-hardware.md — what was ordered and why
• servo-drive-interface.md — the SGDH side of TB5 and TB3
• io-map.md — every machine signal to its wire number