Hallo Oleg,

many datasheets and erratas of '51 derivatives (especially the ones containing Flash!) demand the use of a reset controller which provide correct logic level from Vcc = 0V on. Unfortunately TL77XX series does not work below voltages of 2V, if I remember correctly. This CAN make problems, need not, but can.
As I know, how complicated internal microroutines are when reset modus of microcontroller is invoked, I always use reset controllers, which work at least down to Vcc = 1V. Sometimes I even add additional circuitry, like pull-ups, pull-downs, discrete PMOS or NMOS transistors to guarantee, that reset ciruitry works even at Vcc = 0V. Some parts from MAXIM can be modified by the add of a simple pull-up/down resistor to provide this, also.

I know insisting in this sounds rather paranoid. But I again want to focuse that this issue has been discussed in datasheets, application notes and erratas, several times.

By the way, these disgusting simple RC reset circuits, do show ONE advantage: They provide this performance just by design. May be this is the reason, why they are still recommended in most datasheets, up to today? But not to make any mistake: RC reset circuits are NOT AT ALL recommended by us professionals, because the show many many disadvantages.

Regards,
Kai