MIKROE-455 mikroElektronika, MIKROE-455 Datasheet - Page 25

• Manufacturer Part Number: MIKROE-455
• Description: Development Boards & Kits - 8051 EASY8051 V6 DEVELOPMENT SYSTEM
• Manufacturer: mikroElektronika

Specifications of MIKROE-455

• Rohs: yes
• Product: Development Kits
• Tool Is For Evaluation Of: AT89S8253
• Core: 8051
• Interface Type: CAN, MMC/SD, RS-232, USB
• Operating Supply Voltage: 5 V, 9 V to 32 V
• Data Bus Width: 8 bit
• Description/function: Development Board Only, GLCD, LCD, DS1820, Serial Cable not included
• Dimensions: 265 mm x 220 mm
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 55 C
• For Use With: AT89S8253

Easy8051 v6 Development System
18.0. Port Expander (Additional Input/Output Ports)
The SPI communication lines and MCP23S17 circuit provide the Easy8051 v6 development system with a means of increasing the
number of available I/O ports by two. If the port expander communicates to the microcontroller over the DIP switch SW6 then the
microcontroller pins P3.5, P3.4, P3.7, P1.7, P1.6 and P1.5, used for the operation of port expander, cannot be used as I/O pins.
The microcontroller communicates to the port expander (MCP23S17 circuit) using serial communication (SPI). The advantage of such
MOSI
MISO
SCK
CS
RST
Data transfer is performed in both directions simultaneously by means of MOSI and MISO lines. The MOSI line is used for transferring
data from the microcontroller to the port expander, whereas the MISO line transfers data from the port expander to the microcontroller.
The microcontroller initializes data transfer when the CS pin is driven low (0V). It causes the microcontroller to send clock signal
(SCK) and therefore start data exchange. The principle of operation of the port expander’s ports 0 and 1 is almost identical to the
operation of other ports on the development system. The only difference here is that the port signals are received in a parallel format.
The MCP23S17 then converts such signals into serial format and sends them to the microcontroller. The result is a reduced number
of lines used for sending signals from ports 0 and 1 to the microcontroller and vice versa.
- Master Output, Slave Input (microcontroller output, MCP23S17 input)
- Master Input, Slave Output (microcontroller input, MCP23S17 output)
- Serial Clock (microcontroller clock signal)
- Chip Select (enables data transfer)
- Reset
SPI communication block diagram
Figure 18-1: Port expander
Jumper for selecting
pull-up/pull-down resistor
Jumpers to determine the
port expaner’s hardware
address
PORTB
PORTA
Jumpers J15 are used to determine the port expander’s hardware
address. These jumper are also used to provide the port
expander’s pins A2, A1 and A0 with a logic one (1) or zero (0).
They should be placed in the low position (logic 0) by default.
Figure 18-2: Position of DIP switch SW6
when the port expander is enabled
MikroElektronika
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