MK14 Expansion Connector


The original MK14 has a double sided 32-way edge connector for expansion.  Only the top side is connected (designated B), the bottom side (designated A) is used for connection to the VDU board however the required signals have to be hardwired across the board ! 


The following table shows the signal allocations from the original MK14 schematics (Side B only):


Pin No. Signal Description
1 +5V Power +5V
2 +5V
3 +5V
4 0V Power 0V
5 0V
6 0V
7 0V/NADS 0V on early Issue PCBs and NADS on later issues
8 NADS Address Strobe, when low indicates status and upper four address lines  are on data bus
9 PB6 8154 Port B
10 PB5
11 PB7
12 PB4
13 PB3
14 PB2
15 PB1
16 PB0
17 PA7 8154 Port A
18 INTR Interrupt from 8154
19 PA6 8154 Port A
20 PA0
21 PA5
22 PA1
23 PA4
24 PA2
25 PA3
26 SENSEA Sense A condition input to processor can also be used as interrupt input
27 SIN Serial Input to processor E-register
28 SENSEB Sense B condition input to processor,
29 SOUT Serial Output from processor E-register
30 FLAG0 Flag 0 output from processor
31 FLAG2 Flag 2 output from processor
32 FLAG1 Flag 1 output from processor


The VDU Board has provision for a 64-way DIN41612 connector rather than an edge connector, the following table shows the signal allocations from the original MK14 VDU schematic:


Pin No. Side A
Description Side B
1 0V Power 0V    
2 A0 Lower 12 bits of Address Bus    
3 A1    
4 A2    
5 A3    
6 A4    
7 A5    
8 A6
9 A7 PS1 Page Select Lines
10 A8 PS2
11 A9 PS3
12 A10 PS4
13 A11 VDU OFF VDU on (low) / off (high)
14 A12 Upper four Address allocated but not used GRAPH/CHAR Selects between Graphics (high) and Character (low) modes of operation
15 A13 REVERSE Reverse Pages (low for reverse)
16 A14 INVERT Inverts video output (low for black on white)
17 A15 TOP PAGE Output that is high during first half of frame
18 D0 Data Bus    
19 D1    
20 D2    
21 D3    
22 D4    
23 D5    
24 D6    
25 D7    
27     XOUT 4MHz clock input
28 NRDS Read Data Strobe, data read on trailing edge    
31 NENIN Enable Input, when low processor can access bus    
32 +5V Power +5V    



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