RS530 Technical Reference
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RS530 Interface
RS530 is electrically similar to RS449, but uses a DB25 connector. The smaller connector saves space, and because the DB25 is very commonplace, it is much less expensive.
RS530 employs differential signaling on its send, receive and clocking signals, as well as its control and handshaking signals. The differential signals for RS530 are labeled as either "A and B". At both connectors, wire A always connects to A, and B connects to B.
The RS530 transmitter sends a data 0 (or logic ON) by setting the potential on the A signal to 0.3V (or more) higher than the voltage on the B signal. The transmitter sends a data 1 (or logic OFF) by setting the potential on the B signal to 0.3V or more than the voltage on the A signal. The voltage offset (from ground reference) is not to exceed 3V, however most recievers can handle much more, check the receiver data sheet for exact limits. This approach is relatively immune to noise when the cable is constructed so that the A and B signal wires are a twisted pair. Shielding the cable is generally not required.
| Data 0 = A > B + 0.3V |
| Data 1 = B > A + 0.3V |
| Example: |
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| Data 0 |
A=2V, |
B=1V |
| Data 1 |
A=1V, |
B=2V |
Most receivers can handle both + and - voltages, again check the data sheet on the part used to be sure. If you have the correct receivers it is possible for the older V.35 (+/-5V) signaling to be wired to RS530 or V.11. This is how Cisco and others get many different interfaces on their Smart Serial connectors, and you thought it was magic!
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RS530 Pinout
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PIN
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Signal
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Description
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PIN
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Signal
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Description
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1
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Ground
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Shield
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14
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TDB
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Transmit Data B
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2
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TDA
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Transmit Data A
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15
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TCA
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Transmit Clock A
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3
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RDA
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Receive Data A
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16
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RDB
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Receive Data B
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4
|
RTSA
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Request To Send A
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17
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RCA
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Receive Clock A
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5
|
CTSA
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Clear To Send A
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18
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LL
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Local Loopback
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6
|
DSRA
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DCE Ready A
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19
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RTSB
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Request To Send B
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7
|
GND
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Signal Ground
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20
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DTRA
|
DTE Ready A
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8
|
RLSDA
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Receive Line Signal Detect A
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21
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RL
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Remote Loopback
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9
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RCB
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Receive Clock B
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22
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DSRB
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DCE Ready B
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10
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RLSDB
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Receive Line Signal Detect B
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23
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DTRB
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DTE Ready B
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11
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TTB
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Terminal Timing Clock B
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24
|
TTA
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Terminal Timing A
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12
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TCB
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Transmit Clock B
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25
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TM
|
Test Mode
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13
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CTSB
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Clear To Send B
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| Differential Driver
The resistors Za and Zb are optional. I recommend 10 Ohms to bring the interface to 50 Ohms and to provide some protection from EMI. Note that the "A" signal is on the inverted output pin of the driver, about 50% of designers get this switched in their first design. This happens because some data books call the positive pin A and the negative pin B. The RS530 (RS422) "A" signal must be the inverted pin. This is also true of the receivers.
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| Differential Receiver
The resistor Zt is optional. I recommend 150 Ohms to reduce reflectance. Leave Zt out if you are trying to build a non intrusive receiver. Note that this interface, when left floating, will have an unpredictable output. Some engineers install pull up (to pin A) and pull down (to pin B) resistors of 10k Ohms to provide a known state when the cable is unplugged or connected equipment is turned off.
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