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M Codes

M codes are used for machine control. Here are the most commonly used:

M00 - Full machine stop. Commonly ignored by many plotters.

M01 - Temporary machine stop. Commonly ignored by many plotters.

M02 - End of Plot.

MCU: Microcontroller Unit

A microcontroller unit (MCU) is an integrated circuit (IC) that contains many of the functions found in a typical computer system. A microcontroller uses a microprocessor as its central processing unit and incorporates features such as memory, a timing reference, and input/output peripherals, all on the same chip.

Microcontrollers are very useful in any application in which many decisions or calculations are required. In most cases, it is easier to use the computational power of an MCU rather than use discrete logic. One key advantage of an MCU system is the opportunity to use software to replace complex and expensive logic. One key advantage of an MCU system is the opportunity to use software to replace complex and expensive hardware components. The cost of the initial software development is more than offset by the continued savings in hardware cost and reduced board space.

Typical Microcontroller Application Examples:

 Telephones Answering Machines Pagers Motor Control Appliances Factory Automation Mouse

 Keyboards Stereos Televisions Remote Controls Toys Smartcards Multiplexed Systems

 Anti-lock Braking Systems


MDLC: Message Data Link Controller (J1850 Multiplex)


The Message Data Link Controller (MDLC) incorporates a serial communication multiplex bus that operates according to the SAE J1850 Protocol. Multiple microcontrollers with the MDLC module can communicate over a single or dual wire bus, eliminating the weight and bulk of wire harnesses and adding diagnostic capability.

Some properties of the mdlc module:

 Single Transmit Buffer

 Dual Ping Pong Receive Buffers

 Integrated J1850 VPW Physical Interface

 Supports Messages of Unlimited Length

 Optional CPU Interrupt Capability

 Automatic Transmission Retry Following Loss Of Arbitration

 Supports 10.4KBPS J1850-VPW Communication Only

 Very Low CPU Overhead, Typically 5%

 Power Saving Module Stop and Wait Modes With Optional WakeUp on Network Activity

SAE Standard J1850 Class B Data Communication Network Interface (J1850)

The J1850 protocol encompasses the lowest two layers of the International Standards Organization (ISO) open system interconnect (OSI) model, the data link layer and the physical layer. It is a multi-master system, utilizing the concept of carrier sense multiple access with collision resolution (CSMA/CR), whereby any node can transmit if it has determined the bus to be free. Non-destructive arbitration is performed on a bit-by-bit basis whenever multiple nodes begin to transmit simultaneously. J1850 allows for the use of a single or dual wire bus, two data rates (10.4 kbps or 41.7 kbps), and two bit encoding techniques (pulse width modulation (PWM) or variable pulse width modulation (VPW)).

A J1850 message, or frame, consists of a start of frame (SOF) delimiter, a one- or three-byte header, zero to eight data bytes, a cyclical redundancy check (CRC) byte, an end of data (EOD) delimiter, and an optional in-frame response, followed by an end of frame (EOF) delimiter. Frames using a single byte header are transmitted at 10.4 kbps, using VPW modulation, and contain a CRC byte for error detection. Frames using a one-byte consolidated header or a three-byte consolidated header can be transmitted at either 41.7 kbps or 10.4 kbps, using either PWM or VPW modulation techniques, and also contain a CRC byte for error detection.

Each frame can contain up to 12 bytes (VPW) or 101 bit times (PWM), with each byte transmitted MSB first. The optional in-frame response can contain either a single byte or multiple bytes, with or without a CRC byte. The requirements of each individual network determine which features are used.

MFT: Multi Function Timer

The timer system is used to measure time and to produce signals of specific frequency periods. Timers can be used in multiple ways: The CPU can control the timing of output signals through the output compare mechanism and monitor incoming signals through the input capture mechanism, and the CPU can use the timer system as an internal reference (e.g., delay loops or multiplexing between various software tasks). The timer can be used for virtually any timing function, including waveform generation, simple D/A conversion, and so on.


It is often the case with Gerber data that when moving from one XY coordinate point to another XY coordinate point, the X or Y value will not change. Likewise, it is likely that if the plotter is drawing a line with multiple segments, the segments will be connected and the light stays on from segment to segment.

In both of these cases, there are redundant commands, making the plot data file larger than necessary.

RS-274D allows you to omit this redundant data. This example shows a box being drawn with four corners.

Non Modal Data

Modal Data











From this example, a large amount of data has not been written, thus reducing the final data file size.

ams Advanced Microcomputer Systems, Inc.
10116 NW 53rd St., Sunrise, FL 33351-8020
Phone: (954) 784-0900, Fax: (954) 784-0904



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