Siemens MC55 User Manual download pdf (Page 25)

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Starting up and logging into the GSM network

With no power applied insert your +3V or dual voltage SIM into the card- holder on the solder side

of the board. Connect the antenna cable to the MC55 antenna connector and power up your

PC/104 system. The GPRS6055 will by initialize with the system. After this the status LED will

blink for a while until the MC55 is logged into the network. If you have the PIN code enabled, the

GPRS6055 status LED will continue to blink until the PIN code is given through the terminal mode

with AT command AT+CPIN”XXXX”, unless AT^SFLC (facility lock for PIN code) has been set.

Once the GPRS6055 is logged onto the network the LED will be lit continuously.

INTERRUPTS

What is an interrupt?

An interrupt is an event that causes the processor in your computer to temporarily halt its current

process and execute another routine. Upon completion of the new routine, control is returned to

the original routine at the point where its execution was interrupted.

Interrupts are a very flexible way of dealing with asynchronous events. Keyboard activity is a

good example; your computer cannot predict when you might press a key and it would be a waste

of processor time to do nothing whilst waiting for a keystroke to occur. Thus the interrupt scheme

is used and the processor proceeds with other tasks. When a keystroke finally occurs, the

keyboard then 'interrupts' the processor so that it can get the keyboard data. It then places it into

the memory, and then returns to what it was doing before the interrupt occurred. Other common

devices that use interrupts are A/D boards, network boards, other used serial ports etc.

Interrupt request lines

To allow different peripheral devices to generate interrupts on the same computer, the PC AT bus

has interrupt request channels (IRQ's). A rising edge transition on one of these lines will be

latched into the interrupt controller. The interrupt controller checks to see if the interrupts are to

be acknowledged from that IRQ and, if another interrupt is being processed, it decides if the new

request should supersede the one in progress or if it has to wait until the one in progress has

been completed. The priority level of the interrupt is determined by the number of the IRQ as

follows; IRQ0 has the highest priority whilst IRQ15 has the lowest. Many of the IRQ's are already

used by the standard system resources, IRQ0 is dedicated to the internal timer, IRQ1 is

dedicated to the keyboard input, IRQ3 for the serial port COM2, and IRQ4 for the serial port

COM1. Often interrupts 2,5,7,10,11 and 15 are free for the user.

8259 Programmable Interrupt Controller

The chip responsible for handling interrupt requests in a PC is the 8259 Interrupt Controller. To

use interrupts you will need to know how to read and set the 8259's internal interrupt mask

interrupt controller.

Interrupt Mask Register (IMR)

Each bit in the interrupt mask register (IMR) contains the mask status of the interrupt line. If a bit

is set (equal to 1), then the corresponding IRQ is masked, and it will not generate an interrupt. If a

bit is cleared (equal to 0), then the corresponding IRQ is not masked, and it can then generate an

interrupt. The interrupt mask register is programmed through port 21h

End-of-Interrupt (EOI) Command

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Siemens MC55 User Manual Page 25