User`s manual

724-746-5500 blackbox.com
BL A C K B O X
®
4 of 5
4/13/2010
#14144
With more people using the Internet, new demands have been
placed on computer serial ports. Many PC serial ports aren’t
equipped to handle the level of buffering required for newer data
rates. But advanced UARTs—such as the 16550, 16650, 16750,
and 16850—go a long way toward satisfying the requirements.
Each card has either a UART or an ESCC chip. Universal
Asynchron ous Receiver/Trans mitters (UARTs) are asynchronous
integrated circuits that convert bytes from the com puter bus into
serial bits for transmission. Zilog chips (En hanced Synch ron ous
Communica tions Control lers, or ESCC) are synchronous
inte grated circuits.
I/O addresses and IRQs
All the UARTs in the ISA cards are buffered, so the CPU
is not constantly interrupted to process data.
The adapter is automatically assigned I/O address es and IRQs
by the motherboard. Only the IRQ address can be modified by
the user.
16550 UART
Used in the IC602C, IC110C, IC113C, IC600C, and IC057C,
the 16550 features a 16-byte input and output First-In, First-Out
(FIFO) buffer that holds the characters for the transmitter and
recei ver. The FIFO allows you to obtain higher data rates while
reducing the frequency of pro cess or interrupts. The IC602C
supports speeds up to 400 kbps. All other models with 16550
UARTs support sustained data rates up to 115.2 kbps or bursts
of data up to 460.8 kbps.
16554 and 16C554 UARTs
If you order the IC112C-R3, you’ll receive a card with two
16554 UARTs that con tain four 16550 UARTs, each with a
16-byte FIFO buffer. (The total buffer for the eight ports is
128 bytes.) The IC102C-R2 has a 16C554 UART, which
contains two 16550 UARTs, each with a 16-byte buffer. (The
total card buffer for the four ports is 64 bytes.)
16850 UART
The most popular UART, 16850, is used in IC179C. The
16850 UART has a 128-byte FIFO buffer for each port. This
UART features sus tained speeds of up to 460.8 kbps.
The 16850 UART has FIFO UARTs that enhance communi cations.
They help you avoid the many I/O problems seen in a multitasking
environment—like data overruns or underruns—that occur when
the UART buffering isn’t large enough to handle the in coming
data. These, of course, can interrupt performance and affect your
communications.
The 16850 chip also supports an isochronous scheme, which
is asynchronous framing with an added clock signal. This scheme
allows for much higher data rates and digital-line use (ISDN, T1)
where a clock is supplied for data multiplexing. And you can get
high-speed communications with a simple communications inter face
that responds to standard communi cation calls.
Zilog 85230 ESCC
The IC120C-R4 and IC121C-R3 cards use ESCCs. This chip
operates at speeds of 100 kbps to 1.2288 Mbps.
Technically Speaking