Power, Reset, and Mode Selection Lines

Pin Functions and Descriptions

Line functions defined by the Application Firmware are shown in blue.

Power Supply Requirements

The EM100 should be powered by a stabilized DC power supply with a nominal output voltage of 5V (±5% tolerance). The current consumption of the EM100 is approximately 40mA.

External Reset Considerations

A proper external reset is essential. The reset pulse should be active HIGH. We strongly advise against using low-cost RC networks or other unreliable methods to generate the reset pulse.

The reset should be applied for as long as the power supply voltage is below 4.6V. We recommend using a dedicated reset IC with brownout detection, such as the MAX810. The reset pulse length should be at least 50ms, starting from the moment the power supply voltage exceeds 4.6V.

For added reliability, you may select an external reset IC with a watchdog function. Watchdog reset pulses are provided on the ER line of the EM100.

Reset Control via Host Microcontroller

If the EM100 serves as a communications co-processor in a larger system with its own CPU, it is also acceptable to control the RST line of the EM100 through a general-purpose I/O pin of the host microcontroller. Many microcontrollers’ I/O pins default to HIGH after power-up, which ensures the reset is applied to the EM100 simultaneously with the reset of the host microcontroller. The host microcontroller can release the EM100 from reset at the appropriate time by switching the state of the I/O line to LOW.

MD Pin Functionality

The MD line of the EM100 is used to select the operating mode of the EM100 and/or its application firmware. The signal name in the table above is shown as MD (MD) because its functionality is partly hardwired and partly dependent on the Application Firmware.

Hardwired Functionality

When the EM100 powers up, it checks the state of the MD input:

• If the MD input is HIGH, the EM100 verifies and runs the application firmware loaded into its internal FLASH memory.
• If the MD input is LOW, the EM100 enters serial upgrade mode. For more information, see the Monitor section.

Firmware-Dependent Functionality

Once the application firmware is running, the MD line is typically used to make the EM100 enter serial programming mode. For more details, see the Serial Programming section.

Control of MD Pin by Host Microcontroller

When the EM100 is used as a co-processor in a host system, the MD line can also be controlled by the host microcontroller. The ability to control both the RST and MD lines allows the host microcontroller to switch between the operating modes of the EM100.