MASTECH MAS345

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MASTECH MAS345

The MASTECH MAS345 is a 4000 counts, CAT II handheld digital multimeter with RS232 connectivity.

It is also sold under the names Circuit Specialists CSI3451, Global Specialties Pro-70, McVoice M-345pro, Sinometer MAS345. and Velleman DVM345DI.

1 The software shipped by Circuit Specialists is MasView 1.1.

Hardware

Multimeter:

  • Main chip: MASTECH Japan M343-01 F0951D174 (80 pins, 16 + 16 + 24 + 24)
  • 14-stage binary counter/oscillator: ST 74HC4060 (datasheet) (marking: "ST 74HC4060 N00U732")
  • Precision perational amplifier: Texas Instruments OP07C (datasheet) (marking: "12AL9JM 0P07CP")
  • CMOS multifunctional time base circuit: Green Sea Technology GC7555AP (datasheet, English translation) (marking: "GC7555AP AA7057HS")
    • This is an NE555 compatible chip, apparently.
  • General-purpose photocoupler: Sharp PC817 (datasheet) (marking: "B > B5 PC817 Sharp")
    • "B": model = PC817X2J000F/PC817XF2J00F, ">": China factory, "B5": date code == May 1991
  • General-purpose photocoupler: Sharp PC817 (datasheet) (marking: "B > B6 PC817 Sharp")
    • "B": model = PC817X2J000F/PC817XF2J00F, ">": China factory, "B6": date code == June 1991
  • Crystal: ca. 32kHz
  • Fuse: 15A/250V (6x30mm) (for the 10A jack; interestingly the PCB silkscreen says "20A" for that jack)

RS232 cable:

Photos

Multimeter:

  • Outer package

  • Package

  • Package, open

  • Package contents

  • Device, rubber holster

  • Device, front

  • Device, back

  • Probes

  • Temperature probe

  • LCD

  • LCD w/ backlight

  • Device, open

  • Front cover

  • PCB, front

  • PCB, front, w/o LCD

  • PCB, front top

  • PCB, front middle

  • PCB, front bottom

  • PCB, back 1

  • PCB, back 2

  • LCD 1

  • LCD 2

  • RS232 connector

  • MASTECH M343-01

  • GC7555AP

  • Sharp PC817

  • ST 74HC4060

  • TI OP07C

RS232 cable:

See Device cables#MASTECH_MAS34X_cable.

Protocol

The protocol is (partially) documented in the vendor software's "Help" window (seems to apply to MAS343, MAS344, and MAS345; the M9803R protocol is different).

  • Serial port settings: 600 baud, 7n2, RTS low, DTR high
  • Every time the host sends a (any?) character to the DMM (the vendor software sends D/0x44), it returns 14 ASCII bytes containing the measurement value and so on. The documentation states that a request interval of >= 1 second is "required for stable measuring data from meter".

Packet format:

Byte(s) Description
1-2 Measuring mode (DC, AC, OH, CA, TE, DI, ...)
3 Always a space (?)
4 Sign ('-' or ' ', i.e. a minus or a space)
5-9 Decimal point and current measurement value (Examples: 10.00, 0L, 3.999)
10-13 Unit (Examples: V, mV, A, mA, kOhm, MOhm, nF, ...)
14 Carriage return (13/0x0d)

Example packets:

01 02 03 04 05 06 07 08 09 10 11 12 13 14
D C - 0 0 0 . 0 V \r
A C 0 0 . 0 0 A \r
C A 0 . 0 7 1 n F \r
O H O . L M O h m \r

Resources

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