The IBM Token-Ring module can interrupt the host processor by externally asserting its /INT interrupt that directly drives the /NMRQ NuBus interrupt line. Refer to the Token-Ring data sheet for setting and resetting the interrupt line.
MCP Status Register
Do not use the MCP Status register, it resides at word location C200A. It is provided here for completeness. Its contents are:
Bit Function Notes
--- -------------------------------- ----------------------
7 Last TM1 returned from NuBus
6 Last TM0 returned from NuBus
5 Status of /RESET from NuBus Delayed 4 10MHz clocks
4 Status of "latched reset" signal
3 Not Used, always 0
2 Status of XBACK signal BIAEN* select signal
1 Status of XBG signal
0 Status of XBR signal
Control Register (Pass/Fail LED, and Ring Speed Select)
Read:
. 4-7 3 2 1 0
.-----------------------------------------------------------------------
| Not | IBM chipset | 4/16 Mbps | Yellow-Green | Not |
| Implemented | hard reset | Speed Jumper | LED readback | Implemented |
.-----------------------------------------------------------------------
Write:
. 4-7 3 2 1 0
.-----------------------------------------------------------------------
| Not | IBM chipset | Yellow | Green | Not |
| Implemented | hard reset | LED | LED | Implemented |
.-----------------------------------------------------------------------
One green LED and one yellow LED are provided on the Token Ring NBH/c Card. Upon power-up or any type of reset, both LEDs will clear, indicating that the card is off-line. Once the initialization code has run and determined that the board is operating normally, the green LED will be illuminated by the software writing to the register and reading a speed of 16 Mbps in the speed jumper. If 4 Mbps operation is selected, the Yellow LED should be illuminated. Bit 1 controls the green. A "0" indicates the LED is lit. Bit 2 controls the yellow. A "0" indicates the LED is lit. For diagnostic purposes a logical AND of the LED enables is feedback to bit 1 so that if either LED is on, bit 1 will be active low. To correctly set the LED register, the software should write a 0 to the appropriate bit. For example, to power up the IBM module and turn on the LED for 4Mbps operation, write a byte of $0A at $60001. To power up the IBM module and turn on the LED for 16 Mbps operation, write a byte of $0C.
Also included in this register is the 4/16 Mbps Ring Speed Jumper bit, which passes on the speed selected by the RING SPEED jumper on the card and determines whether the adapter will operate at 4 or 16 Mbps. If bit 2 is set to a 1, 4 Mbps is selected, while a zero means 16 Mbps. This bit is read by the IBM chipset only upon coming out of hard reset.
Bit 3 is connected to the hardware reset line of the IBM chipset. The default is "0", which holds the chipset in the reset state. Upon coming out of reset, the state of the "speed select" bit will be loaded into the chipset. Write a 1 to remove the reset condition.
NuBus Hardware Configuration Register
The NuBus Hardware Configuration Register is not used. Note that this register must be accessed as a word entity.
Non-Optional Registers
The following registers control features of the ACT2441-based NuBus interface which are not used on the Token Ring NBH/c Card. For this reason, only the desired value of each register is listed. The power-up default of all of these registers is 0. These registers must be written with the indicated values to ensure proper functioning of the card:
Address Size Register Value (Hex)
------- ---- ---------------- -----------
C8008 Word External DMA Control 000A
C800D Byte DTACK Control 0 00
C800F Byte DTACK Control 1 07
These locations are the only initialization necessary for correct operation of the Token Ring NBH/c Card.