Keil MCB251, User Manual

Page: 12 / 60

6 Chapter 2. Setup
DIP Switches
The following sections describe each of the DIP switches of the MCB251 board.
Uart_INT: Default ON
The Uart_INT switch selects whether or not the external 16550 UART generates
an interrupt on the microcontroller. If Uart_INT is ON, the interrupt output
from the 16550 is connected to port pin 3.2. If Uart_INT is OFF, the interrupt
output from the 16550 is not connected to the microcontroller. This switch is
useful when using interrupt-driven serial I/O with the external UART. You must
set Uart_INT to ON, if you want to halt execution of a user program within
dScope.
ext_Uart : Default ON
The ext_Uart switch determines whether or not the chip select signal for the
external 16550 UART is generated. If ext_Uart is ON, the chip select signal is
generated and the Monitor program uses the external serial interface for
communication. The communication baud rate is 57600 BPS. If ext_Uart is
OFF, the UART chip select is not generated and the Monitor program uses the
on-chip serial interface for communication. In this case, the communication
baud rate is 19200 BPS.
SRC/D2: Default ON
The SRC/D2 switch selects either SOURCE mode or BINARY mode on the 251
CPU. If SRC/D2 is ON, SOURCE mode is selected. If SRC/D2 is OFF,
BINARY mode is selected.
When you use a 151 or 8051 device, the SRC/D2 must be OFF. When you use
the Dallas 320/520 device, the SRC/D2 must be ON to select a Monitor version
which supports the Dual DPTR registers of that CPU. Refer to “CPU Selection”
on page 10 for a complete description on how to select the CPU type and the
related Monitor version
If you operate the MCB251 with a user application in EPROM, you must set the
SRC/DP2 switch to OFF.