Imported from GitHub: blackbit42/MAUreene_8226 · commit 0eaf286 · license CERN-OHL-P-2.0

Description

Token Ring MAU

README

[!WARNING] The current revision of the board is not functional. Build only if you want to work on fixing it.

Token Ring MAU 'MAUreen'

MAUreene 8226 is a Token Ring (IEEE 802.5) Media Access Unit (MAU) that is inspired by the IBM 8226. For the most part, it is a reproduction of the IBM 8226, reduced to 2 'lobes', which is Token Ring lingo for what is known as a port in the context of other network technologies.

Motivation

Token Ring is an interesting LAN technology. NICs are all over common auction sites and can be had cheaply, though MAUs are hard to come by. The intent of this project is to enable inclined people to play with Token Ring more easily.

Clarification regarding 'crossover' cables

In an ethernet network you can nowadays connect two arbitrary devices with each other back to back without thinking about it, due to to the power of Auto MDI-X. Earlier you could use so-called 'crossover' cables. Unfortunately Token Ring doesn't support such a mode of interconnection, as a NIC goes through a mildly elaborated attachment process with a MAU. A mode where two hosts talk directly to each other doesn't exist, see this.

BOM analysis and mapping

Original 8226	Lobe 1	Lobe 2	Package	Type	Measured value1	Marking	Remarks
R2	R1	R21	0805		4.8k	4871
R10	R2	R22	0603		-None-	-None-	Opto-coupler biasing, not populated
R34	R3	R23	0603		0.3	000	RJ45 termination
R35	R4	R24	0603		0.3	000	RJ45 termination
R44	R5	R25	0603		100	101
R52	R6	R26	0603		100	101
R60	R7	R27	0603			104
R68	R8	R28	0603		10k	103
R76	R9	R29	0603		2k	202
R84	R10	R30	0805		3.7k	3741
R92	R11	R31	0603		4.7k	472	LED series resistor
R96	R12	R32	0603		0.3	000	RJ45 termination
R97	R13	R33	0603		0.3	000	RJ45 termination
C4	C1	C21	1812	Ceramic	330n	-None-
C12	C2	C22	1812	Ceramic	330n	-None-
C20	C3	C23	EIA 7343-31	Tantalum	22u	22-20 LD (2)
C34	C4	C24	0805	Ceramic	120n	-None-
C41	C5	C25	0805	Ceramic	120n	-None-
Q13	Q1	Q21	SOT23	BJT NPN		1P
Q14	Q2	Q22	SOT23	BJT NPN		1P
CR7	D1	D21	SOT23		0.6	A66 (?)	Flyback diode for coil in K2
K22	K1	K21	Non-standard	4PDT		P&B T84S17D214-12
T2	T1	T21	Non-standard	Special Token Ring		Valor PT4043
DS2	-None-	-None-	Non-standard			-None-	LEDs of J1A and J1B are used
L2	-None-	-None-	-None-	-None-		-None-	Unpopulated
U2	U1	U21	DIP-6	Opto-Coupler		QTC H11A1
-None-	J1A	J1B	Non-standard	RJ45 jack

Power supply BOM

Part designator	Value	Description
J200		Barrel jack
J201		2x2 jumper 12V
J202		2x2 jumper 5V
U200		5V linear reg.
C200	0.33uF
C201	0.1uF
C202	0.1uF
R200	495Ohm	12V rail ind.
R201	145Ohm	5V rail ind.

Diode direction

CR7 is in a 3-pin SOT23 package, containing only a single diode. It is connected in parallel with a relay coil, indicating reverse EMF protection for adjacent devices in the circuit. Unfortunately somebody got the direction wrong, hence there is significant reverse EMF with spikes of around 200V. Remarkably, neither the diode itself dies from excessive forward current when the relay is on, nor the switching transistor from the voltage spikes when the relay is being switched off. In the design of this contraption, a diode with normal flyback operation has been foreseen.

Pictures

Photo:

Kicad:

FreeCAD:

X-ray of original PCB, courtesy of @Manawyrm:

Links

https://www.ieee802.org/5/www8025org/

https://ardent-tool.com/network/Understanding_Token_Ring.html

Footnotes

1. Capacitors have been desoldered for measurement with HP 4262A LCR meter. ↩

2. The polarity of the coil supply is reversed, both in the original and this design. Irrelevant, as the relay coils do not have series diodes. ↩