A couple of curiosities I picked up -- APS SCSI Power Plug II. I assume these allow you to 'hot swap' or 'hot power' SCSI devices.
Insides pictured below:
X1 is a 5 MHz crystal.
U11 is a MAX632 step-up voltage regulator
L1 is an inductor needed by the MAX632.
U8, U13 are 74HC00A NAND logic chips
U9, U10 are 74HC74A flip flops
Below:
U1, U2 are Texas Instruments active terminators
U3-U7 are 74HC4066 analog switches
Q1 is a transistor to drive the led
Below: The NT version is the same internally as the regular version, except it is missing the terminator chips. So, NT stands for 'no termination'.
I presume that flipping the switch controls the enable lines on the terminator and analog switch (4066) chips. For example, switching to 'Data GO' disables the termination and enables the 4066 analog switch chips. Thus, the attached device receives the SCSI signals and uses its own termination. Switching to 'Data STOP' enables the termination and disables the SCSI lines from passing through. Thus, it becomes a regular active terminator at the end of the SCSI chain, and the attached device becomes logically disconnected.
For the NT version, I can't imagine a scenario in which you'd want to disable the data lines in the middle of the chain but not provide termination. Perhaps if you want to disable the entire external chain so the Mac thinks nothing is connected externally then you wouldn't want a terminator.
The Maxim MAX632 step up regulator is a bit of mystery. Does it ensure a solid 5V power source for the logic chips? Or can it be enabled/disabled to connect/disconnect termination power from the attached device.
The 5 MHz crystal is also a mystery. U12 is not populated. Perhaps there was a microcontroller here? Or a different type of voltage regulator that needed an external crystal. But, why populate the crystal when U12 is not populated? Or maybe it feeds the NAND/flip flops to provide a delay during the switch?
I don't have any documentation or drivers. But, I figured this was odd enough to be worth posting in case someone actually used them in the past.
- David
Insides pictured below:
X1 is a 5 MHz crystal.
U11 is a MAX632 step-up voltage regulator
L1 is an inductor needed by the MAX632.
U8, U13 are 74HC00A NAND logic chips
U9, U10 are 74HC74A flip flops
Below:
U1, U2 are Texas Instruments active terminators
U3-U7 are 74HC4066 analog switches
Q1 is a transistor to drive the led
Below: The NT version is the same internally as the regular version, except it is missing the terminator chips. So, NT stands for 'no termination'.
I presume that flipping the switch controls the enable lines on the terminator and analog switch (4066) chips. For example, switching to 'Data GO' disables the termination and enables the 4066 analog switch chips. Thus, the attached device receives the SCSI signals and uses its own termination. Switching to 'Data STOP' enables the termination and disables the SCSI lines from passing through. Thus, it becomes a regular active terminator at the end of the SCSI chain, and the attached device becomes logically disconnected.
For the NT version, I can't imagine a scenario in which you'd want to disable the data lines in the middle of the chain but not provide termination. Perhaps if you want to disable the entire external chain so the Mac thinks nothing is connected externally then you wouldn't want a terminator.
The Maxim MAX632 step up regulator is a bit of mystery. Does it ensure a solid 5V power source for the logic chips? Or can it be enabled/disabled to connect/disconnect termination power from the attached device.
The 5 MHz crystal is also a mystery. U12 is not populated. Perhaps there was a microcontroller here? Or a different type of voltage regulator that needed an external crystal. But, why populate the crystal when U12 is not populated? Or maybe it feeds the NAND/flip flops to provide a delay during the switch?
I don't have any documentation or drivers. But, I figured this was odd enough to be worth posting in case someone actually used them in the past.
- David