Editing Amstrad PPC640 (section)

=== Modem ===
The PC2000 modem sits on its own board, PCB901 (MC0053A), and appears to software as COM2: an INS8250 UART at 2F8h on IRQ3.<ref name="ppcsm" /><ref name="trm" /> Amstrad's specification lists V21 (300 bps), V23 (1200/75 bps), V22 (1200 bps) and V22bis (2400 bps), with Hayes commands, auto-dial and auto-answer; the US manual lists Bell 103 and 212A and V22bis.<ref name="ppcsm" /><ref name="ppcui" /> The modem schematics show Rockwell R5325 and R5310 chips (IC901 and IC902), an Am7910 (IC909) and an HD63A01 microcontroller (IC910), with the line transformer marked as a 3000&nbsp;V RMS isolation barrier; the parts list adds the line transformer T901, the relay RL901 and a 0.47&nbsp;µF 250&nbsp;V metallised polyester capacitor, C901.<ref name="ppcsm" /> The Technical Reference Manual withholds the modem's circuit details, citing communications regulations, but the service manual includes its schematics.<ref name="trm" /><ref name="ppcsm" /> Amstrad recommends not using the modem on battery power.<ref name="ppcui" />