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C251: WAIT STATE B ( WSB ) VS EXTENDED DATA FLOAT ( EDF )


Information in this article applies to:

  • C251 All Versions

QUESTION

Looking at the Intel 251SB User's Manual page #71, it shows that UCFG1, bit number 3, has a mnemonic called WSB, and bits 2:1 are called WSB1:0#.

Why did you choose EDF instead of WSB (for bit number 3) as a bit mnemonic inside the START251.ASM?

Here's the section of the start251.asm where I noticed this:

; Extended Data Float (EDF) Timing Feature
; EDF        Val  Description
 ; ----       ---  -----------
 EDF  EQU 0  ; 1 = Standard (Compatibility) Mode
 ;           ; 0 = extend data float timing for slow memory devices

Why is the mnemonic changed from WSB to EDF?

ANSWER

There were 3 steps of the 251: A-Step, B-Step, and C-Step. Only the C-Step devices are currently manufactured.

The WSB bit (UCFG1 bit 3) was used only on the A-STEP parts. It was not used on the B-STEP and C-STEP devices.

The EDF bit (UCFG1 bit 3) was introduced in the 251Tx devices. Refer to the User's Manual Addendum for more information on this bit.

MORE INFORMATION

Last Reviewed: Tuesday, March 27, 2007


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