3C523 Etherlink/MC
3C523 Etherlink/MC TP
Late 3C523 Etherlink/MC
Older versions not compatible with 486+
3C523 ADF Sections

3C523 Etherlink/MC TP

Late 3C523 Etherlink/MC

  I found two of these in a 3172 Interconnect Controller. Marked "(C) 1990 3Com" on the front.

IMPEDANCE
      a.  Use a test device to verify the characteristic impedance of your 
         cable from the wiring closet to the station.
      b.  Choose the setting closest to that characteristic impedance.
          Default Setting:  100 ohms
          Alternative Settings:  75 ohms, 150 ohms

RECEIVE THRESHOLD, LINK BEAT, EQUALIZATION, TRANSMIT LEVEL, and DC SIGNAL jumpers, refer to Table 1. 

 Table 1.  Jumper Settings for 10BASE-T and Non-10BASE-T Hubs

                                         HP StarLAN 10,
                           SynOptics    AT&T StarLAN 10, 
              10BASE-T     LattisNet    DAVID Systems     BULL Hub 10
              (default)  (non-10B-T)    (non-10B-T)       (non-10B-T
Link Beat        ON            OFF             OFF             OFF
Equalization     TX            RX              TX              RX
DC Signal        OFF           ON              OFF             OFF
Xsmit Level      NORM          LOW             NORM            LOW
Rcv Thres        NORM          LOW             NORM            LOW-

3c523 Versions not Compatible with 486+
   The "old" 3C523 have a copyright date of 1987 on them and will only work properly in a 286 or 386. From my expiriences, it will only let the first 8MB RAM be usable no matter how much RAM you have installed.  The newer revision will have a 1990 or 1991 date on it. 

From Peter
   Fact is: some series of the older Ethernet/MC have a microcode incompatible with 486-processors. (Bus signalling most likely - haven't tested that in depth) 
   Symptom: they worked fine as long as they were used in Mod. 70/80 - but when the customer swapped them to the new bought 76/77 they went belly up and did not even pass the DOS-based diags test. 
   These are older ones produced before 1990 - but ironically not all old cards are automatically affected. There was a diagnostic program available from 3COM (I think it came with the revised E/MC) which checks the microcode level and warns for possible incompatibilities. In addition some of the setup / diags and driver software had a problem with later OS-versions (did not run properly under PC-DOS 4.x and above due to "version conflict"). Whatever. 

Component Differences, Old vs. New
>Is that a 3C523? ISTR that those (or most of them, anyway) wouldn't  work properly in anything  than a 386. 

The original 3C-523 has a limitiation - the later ones (3C-523B) hasn't. Roughly the two can be differed by looking on the board: 

Old Model
   Round "transformer", many "through-hole" chips and "classical" resistors, long DIL "i" (Intel) 82586 MCU, "(C) 1987 3Com" at frontside 

New Model
  Square "3Com" transformer, mainly SMD chips with square QFP "i" Intel 82586 MCU, "(C) 1991 3Com" along the bottom/front. 

The old one will most likely not run with anything bigger than a 386DX - the new one hasn't got this problem. Works with 486 and Pentium. Both cards have the same card-ID and use the same ADF, so you cannot tell which is which by the ID only. 

Enable/Disable Adapter
   Use the Disabled setting if you are not using the adapter and enabling it causes a conflict with another device.
     <" Adapter Enabled >, Adapter Disabled 

I/O Address Range
   I/O addresses used by EtherLink/MC. The addresses in this range cannot be used by another installed device
    <"  300 to  307 ">, 1300 to 1307, 2300 to 2307, 3300 to 3307 

Interrupt Level
   Interrupt level used by EtherLink/MC. This adapter's interrupt level can be shared with another device.  You may be able to improve performance
by selecting a level that is not used by any other device.
   <" Channel 3 " ( INT 3)>, 7, 9, 12

Packet Buffer RAM Address Range
   RAM and ROM addresses used by EtherLink/MC.  The addresses in this range cannot be used by any other installed device.  The range represents
16K bytes of RAM addresses followed by 8K bytes of ROM addresses
   <" 0C0000 to 0C5FFF " >, 0D0000 to 0D5FFF , 0D8000 to 0DDFFF

Transceiver Type
   Transceiver used by EtherLink/MC. If you have a thin Ethernet network and wish to connect to the adapter's round BNC connector or you have a twisted pair Ethernet network and wish to connect to the adapter's 8 pin
RJ45 connector (EtherLink/MC TP only), select On-Board.  If you have a drop cable from an external transceiver and wish to attach to the adapter's 15 pin AUI connector, select External.
   <" On-Board (BNC or RJ45) ">, External (AUI)

   NOTE:  If Group 3 tests are running while the computer is connected to an active network, intermittent packet exchange failures may occur before the tests are done.  These failures can be avoided by running Group 3 tests on an inactive network in which only the computer being tested and the echo server are connected.

1.  Make sure adapter is completely seated in slot.
2.  Inspect all cables and connections.
3.  If you are running the Group 2 tests, make sure adapter is securely connected to a loopback plug (coax version only) or to a properly cabled inactive network.
4.  If you are running the Group 3 tests, make sure adapter is securely connected to a properly cabled inactive network and that an echo server is set up on the network.
5.  Make sure that none of the adapter settings conflict with any other    peripheral or software program (such as 3Com's Extended Memory Manager) installed in the computer.  For a list of system resources commonly used by other peripherals, select "Additional Adapter Information" from the main menu, then "System Resources" from the Information submenu. 
6.  Make sure that the transceiver type selected is correct.
7.  Running tests while connected to an active network can cause intermittent failures.  These failures can be avoided by using an inactive network on which only the computer being tested (and an echo server if running the Group 3 tests) is connected.
8.  If you installed an EtherLink/MC TP adapter, check the LEDs on the back-plate of the adapter.  The yellow (ACT) LED is on when there is data
 transmission activity on the adapter.  This light will go on during the Group 2 and Group 3 tests.  The green (LNK) LED will be on when there is a correct connection between the adapter and the hub.  If the link pulse jumper is in the OFF position, the green LED will be on whether or  not there is a connection.
9.  If you have installed an EtherLink/MC TP adapter, make sure that the 
    settings for the following jumpers are correctly configured for the hub:
        RECEIVE THRESHOLD
        DC SIGNAL
        LINK PULSE
        EQUALIZATION
        WIRE IMPEDANCE
        TRANSMIT LEVEL
     For information on setting these jumpers, select "Additional Adapter    Information" from the main menu, then "Twisted-pair Options" from the     Information submenu.
10. The computer slot may be defective.  Install adapter in  another slot and run tests again.
11. The computer in which the adapter is installed may be defective. Install the adapter in a known functioning computer and re-run the tests.
 12. The loopback plug  may be defective.  Try a different loopback plug.
13. Replace failed adapter with a known good EL/MC adapter with the same jumper settings.  If the second EL/MC adapter fails, something is wrong with the test environment, not with the adapter.