CF and '8-bit' IDE

[sae140]

I intend using CF cards in the range 32 - 128 Mb as mass storage with a Z80-based system, and would prefer to use an 8-bit interface to avoid using extra latches etc. So, to save re-inventing the wheel I've been poking around to see what others have done.

Zilog's Advice Note AN015404-0608 demonstrates the use of a 'universal' CF interface (using latches and glue logic - pity) which uses either memory or true-IDE. 8-bit mode in both cases. Their example uses a 64Mb CF card - in which ALL of the memory is accessible in both modes.

Another reference to the successful use of an 8-bit IDE interface is: 8-Bit IDE/ATA Interface (1802 processor) "This circuit provides an 8-bit interface to IDE/ATA devices. This circuit will only allow half of an IDE hard drive to be utilized, unless the device supports the 8-bit mode. CF requires that 8-bit mode be supported. therefore CF cards used on this interface will utilize the full capabiliities of the card."

Which sounds promising ... but I have found 2 references to where this isn't happening in practice:

Simple 8 bit IDE Interface with Compact Flash card. on Flickr - Photo Sharing! (SPECTRUM)
Uses 8-bit IDE - only half of the memory can be accessed

ZX CF interface (SPECTRUM) "On schematic is chip select logic. It is practically same as by 8-bit simple IDE interface. But main advance here is that we work with CF card in memory mode, where data transfer is 8-bit wide, so no capacity loss. Full capacity of CF card is available, while interface remains simple."

So - is there anyone with first-hand experience of using CF cards in 8-bit IDE mode who could advise where the Spectrum guys are perhaps going wrong with 8-bit IDE ? It would be useful to learn from the mistakes (assumption) of others.

'best, Colin

 

[sae140]

Update:

Well, I've dug up some more stuff this morning.

The Compact Flash Association provides support for solid state memory devices as follows ...

"Devices reporting the value 848Ah in IDENTIFY DEVICE data word 0 or devices having bit 2 of IDENTIFY DEVICE data word 83 set to one shall support the CFA feature Set. If the CFA feature set is implemented, all five commands shall be implemented."

- CFA REQUEST EXTENDED
- CFA WRITE SECTORS WIT
- CFA ERASE SECTORS
- CFA WRITE MULTIPLE WIT
- CFA TRANSLATE SECTOR
- SET FEATURES Enable/Disable 8-bit transfer

Well, I read 6 commands, but there you go ....


The one of interest here is:

SET FEATURES register:
01H Enable 8-bit PIO transfer mode (CFA feature set only)

"Enable/disable 8-bit PIO data transfer: Devices implementing the CFA feature set shall support 8-bit PIO data transfers. Devices not implementing the CFA feature set shall not support 8-bit PIO data transfers. When 8-bit PIO data transfer is enabled the Data register is 8-bits wide using only DD7 to DD0."


So - maybe the Spectrum guys aren't programming that facility of the CF card - or could it be that the cards they're using don't support the 8-bit IDE mode ?