Which of the DTMF decoder chips to choose?

Question

Circuit design

The wired telephone should be used as a remote control. Nothing else is needed from him (neither a call, nor voice transmission), a real telephone network from an automatic telephone exchange is also not needed.
Found 3 families of DTMF decoders. Which chip is more suitable for the purposes of "control the controller using tones dialed from the phone"?
MT 3170/3171/3270/3271 Datasheet

Features
• Call progress (CP) detection via cadence indication
• 4-bit synchronous serial data output
• Software controlled guard time for MT3x70B
• Internal guard time circuitry for MT3x71B
• Powerdown option (MT317xB & MT337xB)
• 4.194304MHz crystal or ceramic resonator (MT337xB and MT327xB)
• External clock input (MT317xB)
• Guarantees non-detection of spurious tones
Applications : Integrated telephone answering machine, End-to-end signaling, Fax Machines
Description
The MT3x7xB is a family of high performance DTMF receivers which decode all 16 tone pairs into a 4-bit binary code. These devices incorporate an AGC for wide dynamic range and are suitable for end-to-end signaling. The MT3x70B provides an early steering (ESt) logic output to indicate the detection of a DTMF signal and requires external software guard time to validate the DTMF digit. The MT3x71B, with preset internal guard times, uses a delay steering (DStD) logic output to indicate the detection of a valid DTMF digit. The 4-bit DTMF binary digit can be clocked out
synchronously at the serial data (SD) output. The SD pin is multiplexed with call progress detector output. In the presence of supervisory tones, the call progress detector circuit indicates the cadence (ie, envelope) of the tone burst. The cadence information can then be processed by an external microcontroller to identify specific call progress signals. The MT327xB and MT337xB can be used with a crystal or a ceramic resonator without additional components. A power-down option is provided for the MT317xB and MT337xB.

MT 8870 / 8870D Datasheet

Features
• Complete DTMF Receiver
• Internal gain setting amplifier
• Adjustable guard time
• Central office quality
• Power-down mode
• Inhibit mode
• Backward compatible with MT8870C/MT8870C-1
Applications : Receiver system for British Telecom (BT) or CEPT Spec (MT8870D) -1), Remote control, Telephone answering machine
Description
The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the bandsplit filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low
group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is minimized by on chip provision of a differential input amplifier, clock oscillator and latched three-state bus interface.

CM8870/8870C Datasheet

Features
• Full DTMF receiver
• Industrial temperature range
• Uses quartz crystal or ceramic resonators
• Adjustable acquisition and release times
• CM8870C
— Power down mode
— Inhibit mode
— Buffered OSC3 output (PLCC package only)
• CM8870C is fully compatible with CM8870 for 18-pin devices by grounding pins 5 and 6
Applications: PABX, Remote control, Remote data entry, Call limiting, Telephone answering systems
Description
The CAMD CM8870/70C provides full DTMF receiver capability by integrating both the bandsplit filter and digital decoder functions into a single 18-pin DIP, SOIC, or 20-pin PLCC package. The CM8870/70C is manufactured using state-of-the-art CMOS process technology for low power consumption (35mW, max.) and precise data handling. The filter section uses a switched capacitor technique for both high and low group filters and dial tone rejection. The CM8870/70C decoder uses digital counting techniques for the detection and decoding of all 16 DTMF tone pairs into a
4-bit code. This DTMF receiver minimizes external component count by providing an on-chip differential input amplifier, clock generator, and a latched three-state interface bus. The on-chip clock generator requires only a low cost TV crystal or ceramic resonator as an external component.

What are "guard times" used for and do I need them?

Answer 1

I assembled the circuit on the MT 8870. Somewhere there is even a board layout and a finished device.

Answer 2

yes, MT8870 was also used. Everything worked the first time.