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ISPGDX160VA-7B208 Datasheet(PDF) 4 Page - Lattice Semiconductor |
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ISPGDX160VA-7B208 Datasheet(HTML) 4 Page - Lattice Semiconductor |
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4 / 37 page  4 Specifications ispGDX160V/VA Flexible mapping of MUXselx to MUXx allows the user to change the MUX select assignment after the ispGDXV/ VA device has been soldered to the board. Figure 1 shows that the I/O cell can accept (by programming the appropriate fuses) inputs from the MUX outputs of four adjacent I/O cells, two above and two below. This en- ables cascading of the MUXes to enable wider (up to 16:1) MUX implementations. The I/O cell also includes a programmable flow-through latch or register that can be placed in the input or output path and bypassed for combinatorial outputs. As shown in Figure 1, when the input control MUX of the register/ latch selects the “A” path, the register/latch gets its inputs from the 4:1 MUX and drives the I/O output. When selecting the “B” path, the register/latch is directly driven by the I/O input while its output feeds the GRP. The programmable polarity Clock to the latch or register can be connected to any I/O in the I/O-CLK/CLKEN set (one- quarter of total I/Os) or to one of the dedicated clock input pins (Yx). The programmable polarity Clock Enable input to the register can be programmed to connect to any of the I/O-CLK/CLKEN input pin set or to the global clock enable inputs (CLKENx). Use of the dedicated clock inputs gives minimum clock-to-output delays and mini- mizes delay variation with fanout. Combinatorial output mode may be implemented by a dedicated architecture bit and bypass MUX. I/O cell output polarity can be programmed as active high or active low. MUX Expander Using Adjacent I/O Cells The ispGDXV/VA allows adjacent I/O cell MUXes to be cascaded to form wider input MUXes (up to 16 x 1) without incurring an additional full Tpd penalty. However, there are certain dependencies on the locality of the adjacent MUXes when used along with direct MUX inputs. Adjacent I/O Cells Expansion inputs MUXOUT[n-2], MUXOUT[n-1], MUXOUT[n+1], and MUXOUT[n+2] are fuse-selectable for each I/O cell MUX. These expansion inputs share the same path as the standard A, B, C and D MUX inputs, and allow adjacent I/O cell outputs to be directly connected without passing through the global routing pool. The relationship between the [N+i] adjacent cells and A, B, C and D inputs will vary depending on where the I/O cell is located on the physical die. The I/O cells can be grouped into “normal” and “reflected” I/O cells or I/O “hemi- spheres.” These are defined as: I/O MUX Operation MUX1 MUX0 Data Input Selected 00 M0 01 M1 11 M2 10 M3 Device Normal I/O Cells Reflected I/O Cells B9-B0, A19-A0, D19-D10 B10-B19, C0-C19, D0-D9 B19-B0, A39-A0, D39-D20 B20-B39, C0-C39, D0-D19 ispGDX80VA ispGDX160V/VA ispGDX240VA B29-B0, A59-A0, D59-D30 B30-B59, C0-C59, D0-D29 Table 2 shows the relationship between adjacent I/O cells as well as their relationship to direct MUX inputs. Note that the MUX expansion is circular and that I/O cell B20, for example, draws on I/Os B19 and B18, as well as B21 and B22, even though they are in different hemi- spheres of the physical die. Table 2 shows some typical cases and all boundary cases. All other cells can be extrapolated from the pattern shown in the table. D20 D19 B19 B20 D39 B0 D0 B39 I/O cell 0 I/O cell 159 I/O cell 79 I/O cell 80 Figure 2. I/O Hemisphere Configuration of ispGDX160V/VA Direct and Expander Input Routing Table 2 also illustrates the routing of MUX direct inputs that are accessible when using adjacent I/O cells as inputs. Take I/O cell D23 as an example, which is also shown in Figure 3. |
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