Specifications

PC/II+p Board Technical Reference Manual 65
MT002615 ©1999-2001, Megatel Computer Corporation
7.23 Serial Ports
PC/II+p basic board contains a standard RS-232 port; optionally, a second standard RS-232 port may be
ordered. Each serial port includes a high performance 16C550 compatible UARTs (provided by the ALI
M1543C), and contains an associated Analog ADM211E transceiver. RS-232 serial interface signals are
provided on the Mass I/O Connector, J904.
All serial ports are fully 16C550 compatible and contain send/receive 16-byte FIFOs, standard modem
control and data I/O interface signals, a programmable baud rate generator, and are MIDI compatible. The
I/O ports are configured by the BIOS as COM1 and COM2. COM1 uses Interrupt Request IRQ4, and is
based in I/O address space at 3F8h. COM2 uses Interrupt Request IRQ3, and is based in I/O address space
at 2F8h.
PC/II+p uses the ADM211E receiver/driver on each serial interface to provide RS-232 levels. The transceiver
is EIA-RS232E and CCITT V.28 compliant. Input tolerance on all inputs is ±25V, and output swing on all
outputs is ±9V with all transmitter outputs loaded with 3K ohms to Ground. The transceivers run at +5V and
use on-chip voltage doublers and inverters. Refer to the ADM211E datasheet for determining the power
which may be drawn by attached devices.
Each port contains an independent programmable baud rate generator. The 24 MHz crystal oscillator
frequency reference input is divided by 13, resulting in a frequency of 1.8462 MHz. This frequency is then
divided by a divisor specified in the Divisor register to obtain a frequency which is 16 X the baud rate being
selected. Standard divisors from 50 to 115200 baud are supported. The UART channel ADM211E
transceiver can support speeds up to 230K baud.
Table 33 Serial Channel Baud Rates (From ALI M1543C Datasheet)
Desired baud rate Decimal Divisor for 16X Clock Percent
Error
High speed mode bit in Index
F0h (See ALI documentation)
50
2304 0.1% X
75
1536 0.2% X
110
1047 0.2% X
134.5
857 0.4% X
150
768 0.2% X
300
384 0.2% X
600
192 0.2% X
1200
96 0.2% X
1800
64 0.2% X
2000
58 0.2% X
2400
48 0.2% X
3600
32 0.2% X
4800
24 0.2% X
7200
16 0.2% X
9600
12 0.2% X
19200
6 0.2% X
38400
3 0.2% X
57600
2 0.2% X
115200
1 0.2% X
230400
32770 0.2% 1
Pinouts for the two serial port interfaces are given in Table 34
and Table 35.