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netX design Host
The netX provides a versatile parallel asynchronous interface, referred to as “host interface” or “HIF”, that can either be “active” (netX controls the interface and accesses other memory mapped components) or “passive” (netX behaves like a Dual-Port-Memory (DPM) and is accessed by an external host processor). In DPM mode, the host interface can either be 8 or 16 Bit wide (netX 100/500/50), while the netX 50 also supports 32 Bit mode. Signals that are not used for host interface operation of a design (e.g. upper address lines) can be separately configured as I/Os. The host interface always works in little endian mode.
Due to the fact that the behavior of the netX host interface is configurable to a large extent, most applications do not require any additional glue logic.DPM mode
In DPM mode, the host interface can be controlled by separate Read (RDn) and Write (WRn/WRLn, WRHn) signals (“Intel mode”) or by a combined R/WRn signal indicating the direction of the access and Byte strobe signals (“Motorola mode”). In “Intel mode”, either a single Write signal can be used (WRLn) or two Write signals (WRLn, WRHn) for writing to the low Byte (WRLn) and high Byte (WRHn) separately.
Extension Bus mode
In Extension Bus mode, the netX provides an active parallel, 8- or 16 Bit wide asynchronous bus interface with support for a Ready or Wait signal that allows external components to extend data cycles beyond the programmed cycle timing.
The Extension Bus can either use separate Read (EXT_RDn) and Write (EXT_WRn/WRLn, EXT_WRHn) signals (“Intel mode”) or a combined R/WRn signal indicating the direction of the access along with Byte strobe signals (“Motorola mode”). In “Intel mode”, either a single Write signal can be used (EXT_WRLn), combined with a Byte Enable Signals (EXT_BHEn) or two Write signals (EXT_WRLn, EXT_WRHn) for writing to the low Byte (EXT_WRLn) and high Byte (EXT_WRHn) separately.
The Extension Bus can be used to connect parallel peripherals like SRAMs, FLASHes, DPMs, etc. and can operate in non-multiplexed or multiplexed mode. The four different chip select signals allow to connect four completely different devices, as the configuration for each chip select area is done separately.
The netX also provides the possibility to boot from a memory device connected to the Extension Bus. In that case, the device must be connected to use the EXT_CS0n chip select signal and the Extension Bus boot mode must be selected.
External pull-ups / pull-downs, unused signals
netX 50______________________________________________________________________________
The netX 50 provides internal pull-up resistors on nearly all host interface pins, hence any host interface pins which are not used in a design, may simply be left open. The only exception is the CLOCKOUT signal, which should be equipped with an external pull-up or pull-down (e.g. 10k) when not used, to avoid any cross-currents from a floating signal.
As most host interface control signals are active low, the internal pull-ups usually provide the required inactive level when the netX is in Reset state or when the host interface has not yet been configured by the firmware (all host interface pins are switched to input mode upon reset). However, if for example using an active high interrupt signal, an external pull-down resistor may be required on this signal to avoid an undesired active state (this may also apply to the RDY/WAIT signal, which has a programmable polarity as well).
______________________________________________________________________________netX
50 netX 100/500______________________________________________________________________________
Since even the connected signals of the host interface may float upon reset (they are all configured as inputs by default), designers should make sure, that these initially floating signals will not cause any (start-up) problems with the host interface circuit of their design. If in doubt, add external pull-ups or pull-downs to ensure the appr. inactive state of the signals.
The CLOCKOUT signal and the WDGACT signals should always be pulled low or high when not used, since these signals can not simply be driven low or high. The TCLK signal should always be grounded (this is a dedicated input, so grounding is not a problem).
______________________________________________________________________________netX 100/500