I have used the Winbond W78E58 and W78E516 (and 'LE') devices for some years and can thoroughly recommend them. They have 32/64k appl. flash ROM, 4k ISP loader flash ROM, 256B RAM, 256B XRAM, are available up to 40 MHz, and have the usual standard 8052 features (note W78E58 does NOT have ISP; W78LE58 and W78E58B do). It is also excellent value for money. Its main drawback for some forum people is that the ISP loader ROM area comes unprogrammed, so a device writer is essential for initial use (but see below).

I had an issue (a previous thread) with the security byte, that the datasheet was unclear about: Our HILOSYSTEMS ALL-11 device writer allows us to set the security lock bits to disable readback, external MOVC from internal ROM, and/or readback encryption. Winbond do not seem to give parallel programming information, presumably restricting that info to their favoured writer manufacturers. They do give (somewhat confusing) information on serial ISP programming, but don't say how to re-configure the security byte using ISP mode.

I got really helpful information from Winbond that I should like to pass on to the list. It can be summarised below:
1: The security byte lives in the LDROM (ISP loader flash area) at address FFFFh (the actual loader ROM area is 0000-0FFFh, so this byte is separate from that).
2: It is only resettable to FFh (= no lock bits) by the parallel writer during the application ROM erase cycle.
3: Bits cannot be reset (to '1's) in the ISP mode.
4: They can be set (to '0's) in the ISP mode. So an 'unlocked' device, may be 'locked', for example, under ISP.
5: The security byte can be written/read by setting SFRAH=FFH, SFRAL=FFH, SFRCN=61H/40H, WR/RD data in SFRFD. As you can only write bits to '0', it is only possible to lock; not unlock the device by this method. There is no provision to erase under ISP.
6: If the device is locked (by writer or ISP), it is still possible to perform all functions under ISP. For example, even though the code lock bit is set, code can still be read back for verification from within the ISP function.
7: If, as we do, the lock bit is set during initial parallel programming, we can upgrade the firmware via ISP and the security is retained.

My thanks to my contact at Winbond, who is too modest to give his name, for the information. I believe Winbond are considering pre-programming the LDROM with an ISP loader so that the it will no longer be necessary to initially load the firmware with a writer.

Dave