PB Serial Adapter Provides Full Featured Modem Port for Apple PowerBook 150 and PowerBook 100

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PB Serial Adapter

As of January 1999, we have a few PB Serial Adapters left.

We are selling these off at US$74 each (prepaid by PayPal, cheque, or money order only, no credit cards) including air mail shipping in North America.

Email your intent to order before sending your payment so that we may confirm we have one to reserve for you.

The PB Serial Adapter installs in the modem slot of the Apple PowerBook 100 and 150 (and PowerBook models 140-180) to provide a full feature modem port 8 pin mini-DIN serial connector in lieu of an internal modem.

Some customers have found that using the PB Serial Adapter with an external modem or MIDI device provides significantly better performance compared to using the combination/printer port. (more below)

Is it like a regular modem port?

Yes, the PB Serial Adapter provides the interface normally available on the modem port of Macintosh computers. It provides the Macintosh standard 8 pin mini-DIN connector with RS-422 serial signals, including differential transmit and receive data, two handshake lines, and a general purpose input.

Although the connector looks the same as the combination/printer port, the System software treats the modem port differently. (more below)

External clocking is supported for use with unusual baud rates as is required by MIDI interfaces.

What can I do with it?

With appropriate software, the Serial Adapter can be used with AppleTalk, MIDI, serial printers, external modems and other serial devices. In addition to the standard serial port features, the PB Serial Adapter features very low power consumption and a Wake-On-Ring feature not available elsewhere.

Other PowerBook 140-180 models can also benefit from the PB Serial Adapter in that it provides a simple means to switch between two serial devices on the modem port via the PowerBook Setup control panel, leaving the printer port free for LocalTalk networking.


The PB Serial Adapter includes a wake-on-ring circuit which senses incoming data and requests the PowerBook wake up from sleep mode. This provides the ability to use an external modem for receiving fax messages, as a BBS service, or for serial data collection without having the PowerBook continuously on.

The wake-on-ring circuit senses transitions on the receive data line, thus will trigger on any character or a break signal.

More About Data Rate and Reliability Improvements

Some customers have found that using the PB Serial Adapter with an external modem or MIDI device provides better performance compared to using the combination/printer port. This is due to the Power Manager and other components of Apple's System Software, which treat the combination/printer port as low priority, and the modem port as high priority.

While in certain time consuming portions of the system software (eg. the power manager and floppy disk access), incoming data from the modem port is saved, while combination/printer port data can be lost when it comes in too fast. In most cases, the connection must be above 9600 bps to show the effect.

Measurable improvements depend on the software configuration of the PowerBook, but typically appear as more reliable modem connections (in the sense that fewer blocks are retransmitted due to missed characters), and more reliable MIDI operation (in the sense of missed note-off and other commands).

In extreme cases, customers have found that they cannot maintain a usable SLIP or PPP connection above 9600 bps on the combination port, but can run a reliable connection at 28800 bps via the PB Serial Adapter.


The PB Serial Adapter includes installation instructions. The installation is straightforward but does require some mechanical ability. Although most customers install the unit themselves, some may prefer to have a technical friend help or have an Apple Dealer install the unit for them.


The PB Serial Adapter is warranted against defects in materials and workmanship for 180 days.

Ordering Information

The PB Serial Adapter is available now for US $99 + shipping.

Shipping is typically $7 for Air Mail (1-3 weeks), or $23 for UPS Air (2-3 days) in North America. Canada & BC residents add applicable taxes.

Thank you for your interest, for further inquiries on this product, write to:

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Ruffin Bailey (a real-life customer!) had this to say about Sigma Seven Systems' service:
"Thanks again, and if you ever need some 'happy customer' quote for an advertisement regarding customer service, just stick my name below whatever quote you want!"

There you go Ruffin, now you're famous!

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