Keil MCB251, Руководство пользователя

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16 Chapter 3. Hardware
Status LEDs
The MCB251 has a single power LED labeled ON which indicates the power to
the board is on. Eight LEDs are optionally connected to the Port 1 outputs
through a 74HC373 at IC3. The Port 1 LEDs are flashed during reset and
display the configuration status of the Monitor EPROM. For more information
refer to “Monitor Status Display” on page 11. You may disable the LED driver
by setting the LED DIP switch OFF. The this DIP switch is OFF, the Monitor
does not affect the Port 1 Pins during the reset phase.
Push Buttons
The MCB251 provides two push buttons. The first push button, labeled RESET
(S1), is connected to the reset input of the CPU. The second button, labeled INT
(S2), is connected to the INT1 (port 3.3) of the CPU when the configuration
jumper INT1 (J5) is set. When the configuration jumper NMI is not set, you
may generate an NMI signal to the Temic 251G1 device.
Serial Port
The MCB251 supports both the on-chip serial port and an external UART. Both
use the MAX232, at IC10, to convert TTL to RS-232 voltage levels.
You can configure the Monitor to use either the on-chip serial port or the
external UART for the communication with the PC. When the ext_Uart DIP
switch is ON, the external UART is used at 57600 BPS for the Monitor
communication. Otherwise the on-chip serial port is used at 19200 BPS for the
Monitor communication.
The internal serial port is derived from the internal serial functions of the
8051/251 (P3.0/RXD and P3.1/TXD).
The external UART (IC5) is implemented using an 8250, 16450, or 16550
device. This is the same chip that is used in most PCs. A 1.8432 MHz oscillator
provides the input frequency to the UART. The interrupt output of the UART is
optionally connected to the INT0 pin (port 3.2) of the CPU. When the
Uart_INT DIP switch is ON, the UART interrupt is connected to the INT0 CPU
pin.