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Mastech mas345 device front.png
Status supported
Source code serial-dmm
Counts 4000
IEC 61010-1 CAT II
Connectivity RS232
Measurements voltage, current, resistance, capacitance, temperature, hFE, diode, continuity
Features autorange, data hold, bargraph, backlight

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.



  • 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:


Uses the driver mastech-mas345. You'll generally need the 'conn' driver option to specify the serial device to use.


 sigrok-cli --driver mastech-mas345:conn=/dev/ttyUSB0 --samples 10



RS232 cable:

See Device_cables#Metex_5-pin_RS232_cable.


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).

See Multimeter_ICs#Metex_14-byte_ASCII for the DMM IC protocol.