Agent86
Member
My PDP 11/23 has an M8061 RLV12 RL01/RL02 disk controller, but no disk drive. I've reviewed some excellent drive simulators (Thank you Reinhard) in this forum. Due to component availability, I started laying out a new interface board from from the controller's cable to a commercially available computing platform. Bus termination raised some questions.
The M8061 PCB includes twelve 82 Ohm, 1/2 Watt resistors which I'm inferring are terminators. One for each of the 12 differential signals. If driven at 5 Volts, the power would be V*V/R = 0.305 Watts.
My M8061 has three Texas Instruments SN75113N Dual Differential Line Drivers and three DEC75107B Dual Line Receivers. The 75113 data sheets show a single termination resistor between the differential lines at each end of the bus (transmission line). Termination resistance is called out as Zo, which is meant to match the impedance of the transmission line.
I don't have a DEC cable or terminator and was wondering if anyone has a schematic of the terminator? I'm thinking that the standard DEC cable includes twisted pairs for each of the differential signals. The PDP uses a ribbon cable to attach the M8061 to the backplane of the computer. The backplane also has a ribbon cable compatible connection. I plan to run a ribbon cable, no longer than 1 meter, from my computer to my emulator. I'm guessing that the DEC and M8061 terminators were based on twisted pair transmission line impedance.
My transmission line will probably have a different Zo than DEC's. I won't change the termination resistors on the M8061. My inclination is to mimic the M8061 termination on my PCB - one 82 Ohm resistor across each differential pair.
I know many of you have built, tested, and experimented with these interface boards. I would love to hear what you have to say about proper termination. I would hate to make a mistake which could possibly damage my M8061.
The M8061 PCB includes twelve 82 Ohm, 1/2 Watt resistors which I'm inferring are terminators. One for each of the 12 differential signals. If driven at 5 Volts, the power would be V*V/R = 0.305 Watts.
My M8061 has three Texas Instruments SN75113N Dual Differential Line Drivers and three DEC75107B Dual Line Receivers. The 75113 data sheets show a single termination resistor between the differential lines at each end of the bus (transmission line). Termination resistance is called out as Zo, which is meant to match the impedance of the transmission line.
I don't have a DEC cable or terminator and was wondering if anyone has a schematic of the terminator? I'm thinking that the standard DEC cable includes twisted pairs for each of the differential signals. The PDP uses a ribbon cable to attach the M8061 to the backplane of the computer. The backplane also has a ribbon cable compatible connection. I plan to run a ribbon cable, no longer than 1 meter, from my computer to my emulator. I'm guessing that the DEC and M8061 terminators were based on twisted pair transmission line impedance.
My transmission line will probably have a different Zo than DEC's. I won't change the termination resistors on the M8061. My inclination is to mimic the M8061 termination on my PCB - one 82 Ohm resistor across each differential pair.
I know many of you have built, tested, and experimented with these interface boards. I would love to hear what you have to say about proper termination. I would hate to make a mistake which could possibly damage my M8061.