質問：
What is the pinout for the DB25 serial ports on a VM700A?
回答：
PLEASE NOTE: This article applies to the VM700A models ONLY. If you have a VM700T or a VM700A that has been converted with the Turbo upgrade (to a T model) then please consult the VM700T user manual for connecting your instrument to a PC. The VM700A and VM700T operate differently in this regard.
The pinout for the 25-pin serial ports on the VM700A are as follows:
| Pin | Signal | Notes |
| 1 | Frame Ground | Required for modem connections only. |
| 2 | TD (Transmit Data) | The VM700A transmits data on this pin. |
| 3 | RD (Receive Data) | The VM700A receives data on this pin. |
| 4 | RTS (Request to Send) | When the Flow Control item in the Communications Setup file is set to CTS/RTS, RTS on the VM700A connects to the CTS line of a terminal, and is active when the VM700A is ready to receive data. When the VM700A's receive buffers approach capcity, the RTS goes inactive telling the sending device to stop transmitting data. When the Flow Control item in the Communications Setup file is set to None or XON/XOFF, RTS is always active. |
| 5 | CTS (Clear to Send) | When the Flow Control item in the Communications Setup file is set to CTS/RTS, the VM700A is enabled to transmit data by a high level on CTS, and is disabled by a low level. It is normally connected to the RTS line of a terminal. When the Flow Control item in the Communications Setup file is set to None or XON/XOFF, the VM700A transmits data regardless of the CTS level. |
| 6 | DSR (Sata Set Ready) | Required for modem connections only. Data Set Ready is the modem's equivalent of DTR. When DSR is asserted, the PC/terminal knows it is connected to a "live" modem. |
| 7 | Signal Ground | - |
| 8 | CD (Carrier Detect) | Required for modem connections only. This signal typically comes from a modem and indicates that a connection is made. |
| 20 | DTR (Data Terminal Ready) | Required for modem connections only. This pin is always high when the VM700A is turned on. When DTR is asserted, the modem knows it is connected to a "live" PC/terminal. |
When connecting the VM700A's 25-pin serial connector to a PC's 9-pin serial connector, please connect the following pins:
| VM700A Cable End (25-pin Female) | Flow | PC Cable End (9-pin Demale) |
| 2 – Transmit Data (TD) | > | 2 – Receive Data (RD) |
| 3 – Receive Data (RD) | < | 3 – Transmit Data (TD) |
| 7 – Signal Ground (SG) | - | 5 – Signal Ground (SG) |
| 5 – Clear to Send (CTS) | < | 7 – Ready to Send (RTS) |
| 4 – Ready to Send (RTS) | > | 8 – Clear to Send (CTS) |
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