J64 SFDC

4. Links and Options

Figure 1. Link Positions

Note:
+ = the standard jumper connection, as supplied.
* = the signal is active-low.

This board is described as viewed from the component side with the 64-way bus connector to the right.

LK1 Interrupt Request Line

						Figure 2. Link Area 1.
	LK1A - INTRQ made on ATNRQ0*
	LKIB - INTRQ made on ATNRQ1*		o o o o
	LK1C - INTRQ made on ATNRQ2*		D C B A
	LK1D - INTRQ made on ATNRQ3*		o o o o

LK2 Data Request Line

						Figure 3. Link Area 2.
	LK2A - INTRQ made on ATNRQ4*
	LK2B - INTRQ made on ATNRQ5*		o o o o
	LK2C - INTRQ made on ATNRQ6*		D C B A
	LK2D - INTRQ made on ATNRQ7*		o o o o

LK3 Board addresses

+	LKH	select if A4 low		Figure 4.
+	LKG	select if A5 low		Link area 3
	LKF	select if A6 low
	LKE	select if A7 low		o H o
	LKD2	select if A8 low		o G o
+	LKD1	ignore A8			o F o
	LKC2	select if A9 low		o E  o
+	LKC1	ignore A9			o D2 o D1 o
	LKB2	select if A10 low		o C2 o C1 o
+	LKB1	ignore A10			o B2 o B1 o
	LKA2	select if A11 low		o A2 o A1 o
+	LKA1	ignore A11

Standard jumpering as shown above gives a base address of XC0 (hex) or 192 (decimal), where the x indicates that the top nibble is ignored. Note that some operating systems may not access this board at the standard address. You MUST check with the appropriate software manual.

The board will be selected when a particular combination of address bits and command modifiers is sent to it, with the strobe lines ADRSTB* and DATSTB* active. The command modifiers are those for I/O cycles - CM2 high, CM1 low and CM0 high or low for read or write. The address bits are determined by the jumpering on LK3, which sets what the top eight bits of the address are required to be, and the internal configuration of IC4, which deals with the lower four bits. STEbus I/O accesses use twelve of the twenty address lines.

if any of the jumpers A2,B2,C2,D2,E,F,G,H is inserted, the corresponding comparison address bits (A11 to A4) must be low for the board to be selected, as shown in the table above. For example, consider the base address of the board, which is the address of the status register of the SFDC chip (see Section 5 for more details). If all these jumpers are inserted, the base address is 000. If one of the above jumpers is removed, the corresponding address bit must be high for the board to be selected. Thus, with no jumpers, the base address is FF0. If jumpers A1,81,C1,D1 are inserted, the top 4 bits of the 12-bit address are not used in the comparison, so with these jumpers in, the base address is XF0. With the standard jumpering as indicated above, the base address is XC0.

Another way of looking at the question of address selection is to consider the address lines to have a 'weight', as follows.

Table 1. Address Weights.

Address	Weight
line
	(Hex)	(Dec)
A11	800	2048
A10	400	1024
A9	200	 512
A8	100	 256
A7	 80	 128
A6	 40	  64
A5	 20	  32
A4	 10	  16

A1,B1,C1 and D1 cause the address comparator to ignore that address line when determining if the board is being accessed. If you do not wish to have to set up the top four address lines (for convenience when programming with an 8-bit CPU with a 256 byte I/O map, for example), then make A1,B1,C1 and D1, and leave A2,B2,C2,D2 open. Links A2 to D2, E, F, G and select whether the board responds when that address line is LOW. Leaving them open pulls the corresponding comparator input high, so with no jumpers the address of the SFDC board would start at 4080 decimal (i.e. BASE = 4080 decimal).

LK4 Precompensation

								Figure 5. Link Area 4.

									o
	B	Disable all precompensation.				B
									o
+	A	Enable precompensation on tracks 43 inwards.		A
									o

LK5 Test

LK5 is only made when setting up the SFDC board. It must be left open for normal operation of the board.