Table of Contents


The ECB 4UART-USB board provides four 8250/16C550 similar serial interfaces using the TL16C754B or SC16C754B PLCC chip, which is clocked from 48mhz down to 1.8432mhz. Two of the serial outputs are dedicated to USB ports through a separate FT232RL adapter, and the remaining two outputs may be RS-232 terminal connections, or individually selected as USB connections. Bit rates up to 3mbps are possible, with the proviso that all interfaces use the same clock. With high clock rates, even bit rates down to 110bps are still achievable with large divisors.

Testing indicates that the TL16C754B chips are very sensitive to the relative timing of CSx# and IOW#. CSx# must fall 10ns before IOW#. One way to achieve this is to fit 74ALS139 or 74AHCT139 in place of 74LS139, and use 74LS on the rest of the board (with the exception of the 74F00). SC16C754B does not appear to suffer from this sensitivity.


This board is supported under ROMWBW. It can be enabled by adding the following line to your configuration file:


The following shows the typical ROMWBW output where UART1 - UART4 are the 4UART-USB ports.

RomWBW HBIOS v3.1.1-pre.124, 2021-10-10


UART0: IO=0x68 16550A MODE=38400,8,N,1 FIFO
UART1: IO=0xC0 16650 MODE=38400,8,N,1 FIFO AFC
UART2: IO=0xC8 16650 MODE=38400,8,N,1 FIFO AFC
UART3: IO=0xD0 16650 MODE=38400,8,N,1 FIFO AFC
UART4: IO=0xD8 16650 MODE=38400,8,N,1 FIFO AFC

It can be seen that the default port address starts at 0xC0 and is occupying the range 0xC0 to 0xDF. The corresponding jumpers on the 4uart-usb board are:

0x - Ax : No Jumper
   Cx   : Jumpered
   Ex   : No Jumper

Additionally, the enhanced capability of the chip FIFO buffer and AFC (automatic flow control) are recognized. Note that the driver only supports the default 7.3728 crystal.


The board schematic and board layout are updated from 1.0-002 to 1.0-003 to correct a label error on the RS-232 chip. The erroneous label is MAX239, which is corrected to MAX249. The User Manual got it right. Also, the parts list was posted as a progressive JPG, which the Wiki does not understand. It is reposted as an old JPG, which seems to be okay. It also contains the correction. The physical boards labeled 1.0-002 should have the MAX239 silkscreen label updated to MAX249, and the -002 updated to -003 in ink.

There are no circuit updates as of 30-Mar-2016.


ECB-4UART-1.0-003-sch.pdf 414Kb2016-03-30
ECB-4UART-1.0-003-brd.pdf 491Kb2016-03-30
ECB-4UART-1.0-003-parts_list.jpg 292Kb2016-03-30
ECB-4UART-1.0_manual.pdf 385Kb2016-03-07
TL16C754B datasheet (PDF)675Kb2004-06-01
TL16C754-errata (PDF)41Kb2006-08-01
SC16C754B datasheet (PDF)259Kb2008-10-08
MAX249 page (PDF)66Kb2001-08-01 (Gerbers)283Kb2016-02-28

last update: 30-Mar-2016:::::John Coffman (Gerbers on 2022-10-13)

boards/ecb/4uart-usb/start.txt · Last modified: 2023/02/03 17:02 by jcoffman
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