MICROPROCESSOR (CPU) OPERATION.

TM 11-6625-2975-40

Refer to FO-2 while reading the text in this paragraph.

The microprocessor, also referred to as the central processing unit (cpu), controls all internal signal

generator operations and is contained in cpu assembly A2A1.

The cpu is interconnected with front panel assembly A1, rf modulator assembly A3, and TDM board

A2A3 by a parallel control bus. The control bus is capable of handling 8-bit addresses, 8-bit data,

and I/O read and write pulses. The 8-bit addresses and the I/O read/write pulses are transmitted only

from the cpu while the 8-bit data can be generated by the CPU or, on request, obtained from A1 A1,

A2A3, or A3A3, depending on I/O port addressed.

The 8-bit address selects the correct I/O port. The I/O read pulse strobes data out of the port over the

control bus to the CPU . The I/O write pulse strobes data from the CPU into the correct I/O port via the

control/data bus.

KEYBOARD OPERATION

Every 4 milliseconds the CPU is internally interrupted, and when these interruptions occur, address,

data, and 1/0 write pulses from the cpu are supplied over the control bus to the 1/0 port on the front

panel assembly A1. The I/O port supplies this data to a keyboard matrix, which is scanned to

determine if any keys have been pressed. If the scanner detects any key has been pressed, that data

is returned to the I/O port on the A1 card. Upon request from the cpu, this information is returned to

the CPU over the control bus. The cpu stores this information in memory, but does not act on it until it

receives the same information 12 times in 12 consecutive scanner cycles. On the twelfth cycle, the

cpu recognizes the key entry as valid and proceeds to act on the data stored in memory. In order to

ensure the data is valid and not just key bounce, 12 consecutive cycles are required. Since the key-

board is arranged in a matrix, the data contains the key position in the matrix.

When rf frequency, VOR radial, DDM, or percent modulation entries are made with the keyboard, the

cpu recognizes and stores the data until the DATA ENTRY-ENTER key is pressed. When the cpu

recognizes the ENTER key data, the stored information is processed. If a mistake is made when

entering data, or if an invalid entry is made producing a blinking display, the operator uses the DATA

ENTRY-CLEAR key to clear the CPU memory.

When key activity is not detected by the scanner, the scanner continues to perform its normal routine.

In its normal routine, the scanner:

1. Monitors the keyboard

2. Requests a frequency count from A3 to make sure the frequency displayed is accurate

3. Requests the status of synthesizer phase lock from A3 to make sure the selected rf output

frequency remains phase-locked to the reference frequency

4. Requests the rf level calibration from A3 to make sure the rf level is within specified limits.

At every scanner loop the same information is requested. If the information is not available when

requested, it is obtained during subsequent loops.