Connector for User Interfaces

For the electronic absolute block system

Translation note: Not all terms could be translated. Those terms are marked with a (D) for "Deutsch".

The logic and the user interface part of the electronic absolute block system are connected via a 26 pin plug, "J5". This separation allows a uniform printed circuit board (PCB) for the logic part even with very different types of block prototypes and their model. This specification defines the electrical signals and the pin-out. The corresponding ports of the microcontroller are also listed specifying the interface between the software and the user interface as well.

Connector and Signals

PortPin PinPort
PB4 (B)1112PB5 (B)
PB6 (B)1314PB7 (B)
PC4 (B)1516PC5 (B)
PC6 (B)1718PC7 (B)
  "GND" is the common ground.
"VCC" is the 5 V supply voltage of the logic part. It may be loaded with up to about 100 mA.
"VDD" is the rectified, not stabilized voltage of the power supply. Therefore this voltage is linked to the voltage supplied to the block box.
The ports marked with a "(B)" are controlled via a ULN2803A driver. This is pulling the pin down to GND, allowing a maximum current of 500 mA and a maximum voltage of 50 V. These ports can only drive indicators, buttons may not be connected.
"Clamp" is connected to the common terminal of the free wheeling diodes in the ULN2803A. If inductive loads are connected to at least one output of the ULN2803A, this pin should be connected to the highest voltage used at any output of the ULN2803A (VCC or VDD). In case an external supply is used all inductive loads need individual free wheeling diodes and Clamp may not be connected.

Assignment of Indicators and Buttons

Depending on the type of block different indicators and buttons are needed. The following tables list for each block prototype the assignments of connector pins and therefore microcontroller ports for the indicators and buttons.

Short FormAbsolute Block System Type
AutoAutomatic block system "Selbstblock"
Tf-71Carrier frequency block "Trägerfrequenzblock 71"
Relay Dr-SiemensRelay block for Siemens (D)Drucktastenstellwerke
Relay el.-mech.Relay block for electromechanical signals boxes (e.g. (D)Blockaufbau for an E43)
ManualManual block "Felderblock Form C"

As for double track lines with bi-directional line operation /GWB) two block boards are needed to serve the two station interfaces, the tracks of these lines are treated like two single track lines. Therefore the two track setups are for unidirectional traffic only. The two tracks are labeled "1" for the arrival track (exit block) and "2" for the departure track (entrance block).

Outputs of the ULN2803A

Port Pin  Block Type
Automatic Block   Tf-71     Relay  
Manual NS Blokstelsel
double single track or half GWB line double single double single
PB4  11 BM1 EeM EeM RbM(ye) E(wt)     Wk(wt) Wk(wt)
PB5  12   EaM EaM RbM(rd) E(rd) Stör Stör Stör Stör
PB6  13 BM2 BM BM VbM(ye) A(wt) ÜStör ÜStör ÜStör ÜStör
PB7  14 ASpM ASpM ASpM VbM(rd) A(rd) StrT StrT StrT StrT
PC4  15 Stör Stör Stör StrW(bl) StrW E(rd) E(rd) E(rd) E(rd)
PC5  16 ÜStör ÜStör ÜStör RM BlHTZ   Erl(rd)   Erl(rd)
PC6  17 AzTZ AzTZ E-Sig AsGZ AsTZ A(rd) A(rd) A(rd) A(rd)
PC7  18 Alarm Alarm Alarm Alarm Alarm Alarm Alarm Alarm Alarm

Note: The ports PB5 to PB7 are used for the programming of the microcontroller as well. During programming these ports see fast clocking signals. Therefore only user interface loads, able to tolerate the fast switching without producing excessive noise, should be connected to these ports. Otherwise the user interface has to be disconnected while programming the microcontroller.

Direct Connections to the Microcontroller

Port Pin  Block Type
Automatic Block   Tf-71     Relay  
Manual NS Blokstelsel
double single track or half GWB line double single double single
PA1    2 AzT2 AzT RbT RbT RbT RbT RbT RbT RbT
PA2    3 AzT1 EaT EaT EaT EaT   EaT   EaT
PA3    4 AzGrT AzGrT AsGT AsT AsT   EhT   EhT
PA4    5 E-Sig-nr E-Sig-nr   AsLT AsLT        
PA5    6 E-Sig-ng E-Sig-ng   VbHT VbT VbT VbT VbT VbT
PA6    7 (ÜPrT) (ÜPrT) (ÜPrT) (ÜPrT) blT        
PA7    8       E-Sig StrT BlPrT BlPrT BlPrT BlPrT
PB0  21       Stör As ESpT ESpT ESpT ESpT
PB1  22       ÜStör ÜStör        
PB2  23       EeM Erl(wt)        
PB3  24       EaM Erl(rd)        

Note: In case a single board is used for a double track route (only possible with uni-directional tracks), the ports PB1 to PB3 are used for the station interface and therefore may not be used for the user interface. In case the ports PB1 to PB2 are used in a single track application the two optocouplers U45 and U44 may not be placed on the board!

The implementation of the test button ÜprT is optional. If there is no button, the pin PA6 should be connected permanently to GND. The indicators Stör and ÜStör do not exist in the relay based and the manual block prototypes but are included to notify a broken cable in the model.

A cyan background denotes terminals used as outputs.


  1. TF71
  2. Relay block for (D)Drucktastenstellwerke

List of Abbreviations

A note for the English version: Abbreviations are related to the German version, to keep the labelling of buttons and indicators consistent between the two language versions. Therefore the following table contains the German terms as well.

"I" denotes indicators, "B" Buttons, "A" Alarm, "C" Counter. Alternatively for "I" a colour may be given.

A(rd) (red) entrance block instrument red indicator Anfangsfeld roter Melder
A(wt) (white) Entrance block instrument white indicator Anfangsfeld weißer Melder
As B Activator Anschalter
AsGT B Anschaltgruppentaste
AsGZ C Counter of the activator .......... Zählwerk der Anschaltgruppentaste
ASpM (blue) Exit lock indicator Ausfahrsperrenmelder
AsLT B Activator cancel button Anschaltlöschtaste
AsT B Activator button Anschalttaste
AsTZ C Counter for activator button Anschalttastenzähler
AzGrT B Axle counter reset ...... button Achszählergrundstellungsgruppentaste
AzT B Axle counter reset button Achszählergrundstellungstaste
AzTZ C Counter for Axle counter reset button Achszählergrundstellungstastenzähler
BlGT B Blockgruppentaste
BlHT B Auxiliary block button Blockhilfstaste
BlHTZ C Counter for auxiliary block button Blockhilfstastenzähler
BlPrT B block test button Blockprüftaste
blT (white) blaue Tastensperre
BM (red) Block indicator Blockmelder
E(rd) (red) exit block instrument red indicator Endfeld roter Melder
E(wt) (white) Exit block instrument white indicator Endfeld weißer Melder
EaM (yellow)permission passed indicator Erlaubnisabgabemelder
EeM (yellow)permission receipt indicator Erlaubnisempfangsmelder
EaT B permission passing button Erlaubnisabgabetaste
EhT B permission taking button Erlaubnisholentaste
EM I permission indicator Erlaubnismelder
Erl(rd) (red) permission block instrument red indicator Erlaubnisfeld roter Melder
Erl(wt) (white) permission block instrument white indicator Erlaubnisfeld weißer Melder
E-Sig (red) entrance signal stop indicator Einfahrsignalhaltmelder
E-Sig-nr (red) next station entrance signal stop E-Sig Halt der Nachbarbetriebsstelle
E-Sig-ng (green) next station entrance signal clear E-Sig Fahrt der Nachbarbetriebsstelle
ESpT B Entsperrtaste
MJ I I Motor inductor I (button and fault indicator) Motorinduktor I (Taste und Störmelder)
MJ II I Motor inductor II (button and fault indicator) Motorinduktor II (Taste und Störmelder)
MJ I/II I Reset button for the
motor inductors I & II
Grundstellungstaste für die
Motorinduktoren I & II
I Power line indicator Netzüberwacher
RbHGT B Rückblockhilfsgruppentaste
RbM(ye) (yellow) Rückblockmelder(gelb)
RbM(rd) (red) Rückblockmelder(rot)
RbT B Rückblocktaste
RM (yellow)Clearance indicator Räumungsmelder
SpT B Lock button Sperrtaste
SpZ C Counter of lock button Zählwerk der Sperrtaste
Stör (red) Fault indicator Störmelder
StrT (white) Clearance lock Streckentastensperre
StrW (red) Streckenwiederholungssperre
StrW(bl) (blue) Streckenwiederholungssperre
ÜPrT B Block transmission test button Blockübertragungsprüftaste
ÜStör (red) Block transmission fault indicator Blockübertragungsstörmelder
ÜStörZC Counter for block transm. test button Zählwerk der Blockübertragungsprüftaste
VbM(ye) (yellow)Pre-block indicator(yellow) Vorblockmelder(gelb)
VbM(rd) (red) Pre-block indicator(red) Vorblockmelder(rot)
VbT B Pre-block button Vorblocktaste
VbHT B Auxiliary pre-block button Vorblockhilfstaste
Wk(wt) (white) permission request indicator Erlaubnisanforderungssmelder
WUT B Alarm interrupt button Weckerunterbrechertaste
Zs I Train end indicator Zugschlußmelder

Valid HTML 4.0!