2 Feb
2025
2 Feb
'25
7:04 p.m.
On 02/02/2025 18:32, Paul Koning via cctalk wrote:
On Feb 1, 2025, at 5:57 PM, Chuck Guzis via cctalk
<cctalk(a)classiccmp.org> wrote:
74HC run on +5V is not the same as TTL, which I fell over recently. The
CMOS version can push the output to Vcc whereas TTL can't quite get
there. Sometimes it matters - and in the spirit of the RS232 thread, I
was interfacing TTL to an ISP interface on an old MCU, which is done
using TTL level "RS232"; and you can have DTR flip it into programming
mode. Except the "switch to programming mode" pin on the MCU really did
need to be Vcc high, not the TTL '1' that the DTR line on the
USB->Serial adapter was putting out.
Buffered it through an HC gate and the cable worked.
74C (without the H) has a much wider supply voltage range (same as 4000
series)
Shame no one else hereabouts used minilogs :-(
On 2/1/25 13:31, Frank Leonhardt via cctalk
wrote:
Similarly, early CMOS logic IC, both the original Philips 4000 series and the 74HC
series, support a surprisingly wide range of supply voltages. 3-15 volts for the 4000
series (according to my Radio Shack reference that is), 2 to 6 volts for 74HC. The speed
drops off dramatically with lower voltages, though, as I found out when using a 74HC bus
driver in a 3.3 volt logic design.
paul
I started with minilogs which were +/- 10V
logic.
Anyone remember those?
I remember HTL (15V) being basically a high-voltage version of DTL.
--Chuck