The original serial port driver for the Macintosh, as documented in Inside Macintosh, only allowed settings of up to 57.6 kbps on the serial ports. This speed is usually not attainable by the older 68xxx Macintosh systems. With the introduction of SerialDMA architecture, present in the 660AV and 840AV systems, Power Macintosh models, as well as PowerBook 3400 (with the exception of the 5200, 6200, 5300, 6300, and PowerBook 1400, and 5300 systems) it may be possible to drive the serial ports at speeds up to 230.4 kbps.
The SerialDMA 2.0.2 driver documentation describes these higher speed control calls. In the future, we expect to see updated tools that take advantage of these higher speed calls. Since the Macintosh Toolbox only allowed a maximum setting of 57.6 kpbs nearly all communications software, such as the Apple Modem Tool and the Serial Tool, use 57.6 kbps as the maximum.
A PC Card modem is not subject to the same limitations as communications through a serial port. Since PC Cards can handle 10 Mbs Ethernet connections it is certain that unless the manufacturer has done some very poor engineering, the only limitation is the ability of the modem to handle the data throughput.
Note: System 7.5.3 includes a new version of Apple Modem Tool (1.5.5), which supports 115.2K and 230.4K connections on SerialDMA 2.0 machines.
This article appeared in the 17 May 1996 issue of Information Alley.