Power, Reset, and Mode Selection Lines*

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#3

VCC

Input

Positive power input, 5V nominal, +/- 5%, app. 40mA

#8

GND

 

Ground

#11

RST

Input

Reset, active high

#14

MD (MD)

Input

Mode selection pin

Line functions defined by the application firmware are shown in blue

 

The EM100 should be powered from a stabilized DS power supply with output nominal voltage of 5V (+/- 5% tolerance). Current consumption of the EM100 is approximately 40mA.

 

Proper external reset is a must! Reset pulse should be an active HIGH. We strongly advise against using low-cost RC-networks and other unreliable methods of generating reset pulse. 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 MAX810. Reset pulse length should be no less than 50ms, counting from the moment the power supply voltage exceeds 4.6V.

 

For added reliability, external reset IC with watchdog function may be selected. Watchdog reset pulses are provided on the ER line of the EM100.

 

If the EM100 is used to serve as a communications co-processor in a larger system that has its own CPU it is also OK to control the RST line of the EM100 through a general-purpose I/O pin of the "host" microcontroller. I/O pins of many microcontrollers default to HIGH after the powerup and this means that the reset will be applied to the EM100 at the same time when the host microcontroller is reset. All the host microcontroller has to do is release the EM100 from reset at an appropriate time by switching the state of the I/O line to LOW.

 

The MD line of the EM100 is used to select the operating mode of the EM100 and/or its application firmware. The reason why the pin name is shown as MD(MD) is because the functionality of this pin is in part hardwired and in part depends on the application firmware:

 

Hardwired functionality. When the EM100 powers up it verifies the state of the MD input. If the MD input is at HIGH the EM100 proceeds to verifying and running the application firmware loaded into its internal FLASH memory. If the MD input is at LOW the EM100 enters the serial upgrade mode. For more information see Monitor.

 

Application firmware-dependent functionality. When the application firmware is already running the MD line is typically used to make the EM100 enter the serial programming mode. For more information see serial programming.

 

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