AR# 7697


CPLD XPLA - What are the differences between ABEL and PHDL?


Keywords: XPLA Professional, CoolRunner, fitter, ABEL, PHDL, differences

Urgency: Standard

General Description:
What are the differences between ABEL and PHDL?


PHDL (formerly Philips Hardware Description Language) is a sub-set of ABEL.

Most PHDL designs should compile without modification (except for changing the
file extension to .abl) in Xilinx Project Navigator. The only exception to this are the
dot extensions .X1 and .X2 that are supported in PHDL to support the hardware
XOR function in CoolRunner XPLA2 (960 and 320 macrocell devices) CPLDs.

The most complete description of PHDL can be found in Chapters 5 and 6 of the
XPLA Professional User's Manual at:

The following table shows ABEL features that are either ignored or not supported
in PHDL:

ABEL and PHDL Differences
ABEL and PHDL Differences

It is important to note that the PHDL compiler will do syntax checking on signals that
have register attributes (reg, reg_d, reg_g, reg_jk, reg_sr, and reg_t) to insure that
these signals have a clock (.clk) assignment and a consistent input assignment (.d for
reg_d, .t for reg_t). If a signal with a register attribute does not have clock assignment
or has an inconsistent input assignment statement, an error is generated. This syntax-
checking with register attributes is not done in ABEL.

Also note that CoolRunner CPLDs do not have an inverter between the macrocell and
the output pin. Therefore, the INVERT attribute results in the inverter being emulated in
the equations for the register input, and equations for AR and AP are swapped.

However, since CoolRunner 22V10s do have an inverter between the macrocell and
the output pin, the INVERT attribute is handled as expected. The INVERT attribute
has no meaning for combinatorial signals.
AR# 7697
Date 01/29/2009
Status Archive
Type General Article
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