M
[email protected]
- Jan 1, 1970
- 0
Hello.
I am in need of recommendations on how to design a properitary MDB to
RS232 hardware interface. I want to use a laptop running a custom
visual basic interface/diagnostics program, and interface it with a
proprietary multi drop bus on a ticket vending machine.
I don't think the MDB in question conforms to RS485 or RS422 otherwise
this wouldn't be such a difficult task. I just want to read and write
to the MDB (master) using a serial port (slave) on a laptop. Based on
the specs of the MDB listed below, what do I need to do? Use
opto-isolators because of the current loop design? What about voltage
conversion? Timing/Clock issues? See section 4.2 below.
Thanks for any help.
MDB Specs:
-----------------------------------
2.1 BYTE FORMAT
Baud Rate: 9600 NRZ
Serial Bit Format: 1 Start Bit
8 Data Bits
1 Mode Bit
1 Stop Bit
11 Bits Total
LSB MSB
Start 0 1 2 3 4 5 6 7 Mode Stop
Mode Bit: Master-to-Peripheral
The mode bit differentiates between ADDRESS bytes and DATA bytes.
ADDRESS bytes must be read by all peripherals, DATA bytes are only
read by the peripheral that has been addressed.
The mode bit is set (logic one) to indicate an ADDRESS byte, and not
set (logic zero) to indicate a DATA byte.
Mode Bit: Peripheral-to-Master
The mode bit must be set on the last byte sent when data is sent from
a Slave to the Master.
3.2 TIMING SPECIFICATIONS
Baud Rate = 9600 +1%/-2% NRZ
t = 1.0 mS
inter-byte (max.)
t = 5.0 mS
response (max.)
t = 100 mS
break (min.)
t = 200 mS
setup (min.)
NOTE: All peripherals have the option of not responding to the VMC.
Non-response timing is defined in the peripheral specification.
Hardware Specification
4.1 BUS POWER SUPPLY DEFINITION
The information below defines the minimum VMC voltage output. The
actual current ratings per peripheral will be defined in their
respective sections.
Power supply filtering is optional, therefore if a peripheral requires
more power, or tighter regulation, they may elect to supply their own
power, or filtering, from available sources elsewhere in the machine.
VMC Voltage Output:
Minimum = 20 VDC rms. (rectified and optionally filtered)
Nominal = 34 VDC unreg. (rectified and filtered)
24 VDC rms. (rectified only)
Maximum = 42.5* VDC (ripple voltage upper limit)
*High line input may allow 45 VDC peak (max.).
4.2 BUS TRANSMITTER / RECEIVER SPECIFICATION
The following section describes the 5V, optically isolated, current
loop system between the Master and the Slave.
VMC Master:
Transmit:
Minimum source current (active): 100 mA @ 4V
Maximum leakage current (inactive): 100 uA
NOTES: 1) The transmit line must be able to withstand a short while
in the active mode.
2) 15 mA should be added for each peripheral over six.
Receive:
Minimum input current (active): 15 mA @ 1V
Maximum input current (inactive): 1 mA
Peripheral Slave:
Receive:
Maximum input current (active): 15 mA @ 4V
Maximum input current (inactive): 100 uA
Transmit:
Minimum sink current (active): 15 mA @ 1V
Maximum leakage current (inactive): 30 uA
I am in need of recommendations on how to design a properitary MDB to
RS232 hardware interface. I want to use a laptop running a custom
visual basic interface/diagnostics program, and interface it with a
proprietary multi drop bus on a ticket vending machine.
I don't think the MDB in question conforms to RS485 or RS422 otherwise
this wouldn't be such a difficult task. I just want to read and write
to the MDB (master) using a serial port (slave) on a laptop. Based on
the specs of the MDB listed below, what do I need to do? Use
opto-isolators because of the current loop design? What about voltage
conversion? Timing/Clock issues? See section 4.2 below.
Thanks for any help.
MDB Specs:
-----------------------------------
2.1 BYTE FORMAT
Baud Rate: 9600 NRZ
Serial Bit Format: 1 Start Bit
8 Data Bits
1 Mode Bit
1 Stop Bit
11 Bits Total
LSB MSB
Start 0 1 2 3 4 5 6 7 Mode Stop
Mode Bit: Master-to-Peripheral
The mode bit differentiates between ADDRESS bytes and DATA bytes.
ADDRESS bytes must be read by all peripherals, DATA bytes are only
read by the peripheral that has been addressed.
The mode bit is set (logic one) to indicate an ADDRESS byte, and not
set (logic zero) to indicate a DATA byte.
Mode Bit: Peripheral-to-Master
The mode bit must be set on the last byte sent when data is sent from
a Slave to the Master.
3.2 TIMING SPECIFICATIONS
Baud Rate = 9600 +1%/-2% NRZ
t = 1.0 mS
inter-byte (max.)
t = 5.0 mS
response (max.)
t = 100 mS
break (min.)
t = 200 mS
setup (min.)
NOTE: All peripherals have the option of not responding to the VMC.
Non-response timing is defined in the peripheral specification.
Hardware Specification
4.1 BUS POWER SUPPLY DEFINITION
The information below defines the minimum VMC voltage output. The
actual current ratings per peripheral will be defined in their
respective sections.
Power supply filtering is optional, therefore if a peripheral requires
more power, or tighter regulation, they may elect to supply their own
power, or filtering, from available sources elsewhere in the machine.
VMC Voltage Output:
Minimum = 20 VDC rms. (rectified and optionally filtered)
Nominal = 34 VDC unreg. (rectified and filtered)
24 VDC rms. (rectified only)
Maximum = 42.5* VDC (ripple voltage upper limit)
*High line input may allow 45 VDC peak (max.).
4.2 BUS TRANSMITTER / RECEIVER SPECIFICATION
The following section describes the 5V, optically isolated, current
loop system between the Master and the Slave.
VMC Master:
Transmit:
Minimum source current (active): 100 mA @ 4V
Maximum leakage current (inactive): 100 uA
NOTES: 1) The transmit line must be able to withstand a short while
in the active mode.
2) 15 mA should be added for each peripheral over six.
Receive:
Minimum input current (active): 15 mA @ 1V
Maximum input current (inactive): 1 mA
Peripheral Slave:
Receive:
Maximum input current (active): 15 mA @ 4V
Maximum input current (inactive): 100 uA
Transmit:
Minimum sink current (active): 15 mA @ 1V
Maximum leakage current (inactive): 30 uA
