Casio EG-800U - Cassiopeia - Win CE 3.0 150 MHz Specifications download pdf (Page 8)

SLAA137A

8 MSP430 Internet Connectivity

MSP430F149 CS8900A

D[7..0]

A[3..0]

IOR

IOW

Isolation

Transformer

RJ45

Connector

LEDs: Power,

Link, LAN

20 MHz8 MHz

JTAG

Figure 3. Hardware Block Diagram

3.1 Interfacing to the LAN Controller

The most interesting thing is the connection between the LAN controller (IC2) and the MCU

(IC1). The CS8900A can operate in three different modes: I/O space, memory space, and as a

DMA slave. All of these modes have their special advantages and disadvantages. For this

project, the I/O space operation mode is the best choice. This is the default mode and is always

enabled. The most important fact is that it is possible to use an 8-bit width data bus (see

Resource [10] for a detailed description). This data bus is connected to general I/O-port 5 of the

MSP430. The CS8900A in I/O mode is accessed through eight 16-bit I/O ports that are mapped

into 16 registers. To access them, a 4-bit address bus width is used. There are also two control

lines used, IOR and IOW. These signals are active-low and indicate whether there is a read or a

write access in progress. The whole interface is implemented by using only 14 electrical signals.

All unused pins of the CS8900A are driven to appropriate levels to choose the operating mode

and configure the bus interface. For example, after any reset the CS8900A responds to default

I/O address 0x300. The address lines that are not changed while accessing this I/O address are

hardwired to 0x300.

After applying a valid I/O address to the address bus and driving one of the control lines (IOR,

IOW) to low, data transfer over the data bus can take place.

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Casio EG-800U - Cassiopeia - Win CE 3.0 150 MHz Specifications Page 8