The MM5203 required -50V for programming.
The 2708 required a nominal +26V, but +25V would also work.
That brings back memories from 1975
I've had to build programmers for both these chips, but the MM5203 was the most nerve wracking because they were so expensive to blow up back in the day.
And I blew up a few getting the programmer working properly.
The programmer had to be made with TTL and analog parts because I didn't have a handy MCU to throw at it like nowadays.
Here is a online scan of the MM5203 programming process for any other 'greyhairs' wanting a walk down memory lane.
https://archive.org/stream/bitsavers_nationaldaMemoryDatabook_43572148/1977_National_Memory_Databook_djvu.txtOperation of the MM4203/MM5203 in program mode
Initially, all 2048 bits of the MM4203/MM5203
are in the HIGH state. Information is introduced
by selectively programming LOWS in the proper
bit locations. (Note!)
Word address selection is done by the same decod-
ing circuitry used in the Read mode. The eight
output terminals are used as data inputs to deter-
mine the information pattern in the eight bits of
each word. A LOW data input level (-50V) will
leave a HIGH and a HIGH data input level will
allow programming of a LOW All eight bits of one
word are programmed simultaneously by setting
the desired bit information patterns on the data
input terminals. The duty cycle of the Vdd pulse
(amplitude and width as specified on page 4)
should be limited to 2%. The address should be
applied for at least 1 jus before application of the
Program pulse. In programming mode, data inputs
1-8 are pins 4-11 respectively regardless of the
logic state of Ag and mode control. Chip select
should be disabled (HIGH).
Positive logic is used during the read miode for
addresses and data out. Address 0 corresponds to
all address inputs at V,l and address 255|o cor-
responds to all address Inputs at V|^^. A “1" or a
P at a data output corresponds to Vqh- A "0” or
an N at a data output corresponds to \/Q^_. Posi-
tive logic is also used during the programming mode
for addresses. Address 0 corresponds to all address
inputs at V,Lp and address 255 iq corresponds to
all address inputs at V|Hp.
Negative logic is used during the programming mode
for data in. A "1" or a P at a data input corres-
ponds to V|L,p. A "0” or an N at a data input
corresponds to V|Hp.