Specifications

DV 15 - SCSI Termination Page: 4
* "...an active termination circuit automatically terminates the [internal device] when it is the last device on the bus. If a
terminated device is attached to the external SCSI port, the internal termination is deactivated."--p. 18 of Macintosh IIvx,
IIvi, Performa 600 Developer Note.
"The Macintosh Centris 610, Macintosh Centris 650, and Macintosh Quadra 800 computers include a new feature that
automatically provides the proper termination when no external device is connected. . . . When one or more devices are
connected, the circuitry detects the external termination during system reset and disconnects the termination on the logic
board."--p. 19 of Macintosh Centris 610, Macintosh Centris 650, and Macintosh Quadra 800 Computers Developer Note.
Termination on Apple Printers
The Apple LaserWriter IIf and IIg and Apple LaserWriter Pro 630 printers require the same terminator as the
IIfx--Apple SCSI Terminator II (M5871G/A)--when connecting up to seven external SCSI storage devices (which are for
storing downloadable fonts, not for connecting the printer to a Macintosh).
The LaserWriter Pro 630 is the first Apple LaserWriter that can also take a single internal SCSI hard drive (for font
storage) in addition to six (for a total of seven) external hard drives. Any internal drive must not be terminated
internally since permanent termination is supplied on the motherboard. This termination cannot be removed. The internal
hard drive's SCSI ID is hardwired to the motherboard; it is ID 6. Since this drive also counts as one of the seven total
devices allowed on the bus, any external device must not have SCSI ID 6 when the internal drive is present. If no internal
hard drive is present, SCSI ID 6 is still reserved--external SCSI devices may not use ID 6 even if no internal hard drive
is present. The end of the external SCSI chain must also be terminated, whether an internal drive is present or not.
The LaserWriter Pro 630 does supply termination power (TPWR) to the internal device but not to external devices. The
LaserWriter IINTX, IIf, and IIg printers do not supply TPWR.
The Apple LaserWriters IINTX and IINTXJ require the standard, gray Apple terminator (M0332LL/A) when connecting
external storage devices.
The Apple Personal LaserWriter SC and IISC printers as well as the Apple Color Printer are SCSI devices themselves; that
is, rather than being networkable printers, they connect directly to the SCSI bus of the Macintosh. These printers require
the standard, gray Apple terminator, unless you're using them with a Macintosh IIfx, in which case you should use the
black terminator. In other words, for the SCSI printers (only), the termination requirements are dictated by the
Macintosh since the printer functions as just another SCSI device on the Macintosh computer's SCSI bus.
Below is a chart that will help you determine the termination characteristics of all of Apple's printers. Printers with no
SCSI implementation are included just for the sake of completeness, so those characteristics that do not apply will list
n/a, for "not applicable," under the appropriate heading(s).