The Busing Network
Figure 3 on page 7 depicts one of five identical busing planes. Each plane has three bus
resources: a local-bus resource (the middle bus) and two express-bus (both sides)
resources. Bus resources are connected via repeaters. Each repeater has connections
to two adjacent local-bus segments and two express-bus segments. Each local-bus
segment spans four cells and connects to consecutive repeaters. Each express-bus
segment spans eight cells and “leapfrogs” or bypasses a repeater. Repeaters regener-
ate signals and can connect any bus to any other bus (all pathways are legal) on the
same plane. Although not shown, a local bus can bypass a repeater via a programma-
ble pass gate allowing long on-chip tri-state buses to be created. Local/Local turns are
implemented through pass gates in the cell-bus interface. Express/Express turns are
implemented through separate pass gates distributed throughout the array.
Some of the bus resources on the AT40K/AT40KLV are used as a dual-function
resources. Table 2 shows which buses are used in a dual-function mode and which bus
plane is used. The AT40K/AT40KLV software tools are designed to accommodate dual-
function buses in an efficient manner.
Table 2. Dual-function Buses
Function
Type
Plane(s) Direction
Comments
Cell Output Enable
Local
5
Horizontal
and Vertical
RAM Output Enable Express
2
Vertical
Vertical
Vertical
Bus full length at array edge
Bus in first column to left of
RAM block
RAM Write Enable
RAM Address
Express
Express
1
Bus full length at array edge
Bus in first column to left of
RAM block
1 - 5
Buses full length at array edge
Buses in second column to left
of RAM block
RAM Data In
Local
Local
1
2
Horizontal
Horizontal
Data In connects to local
bus plane 1
RAM Data Out
Data out connects to local
bus plane 2
Clocking
Express
Express
4
5
Vertical
Vertical
Bus half length at array edge
Bus half length at array edge
Set/Reset
6
AT40K/AT40KLV Series FPGA
0896C–FPGA–04/02
ATMEL [ ATMEL ]
