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Hi Don,
Yes, the MAX232 chips could be used. Someone else pointed out that if I were to use an 8085 with MAX232 chips, we wouldn't even need the +12/-12 and -5V regulators, saves a lot of space. However, the 8080 was chosen because it provides all the status signals that the ALTAIR and IMSAI front panels display. The MAX232 chips could be used, but there would not be any real space savings. The MAX 232 offers 4 gates (2 transmit, 2 receive) in a 16 pin package. The 1488 offers 4 transmit in a 14 pin package and the 1489 offer 4 receive in a 14 pin dip. If you are only going to use Transmit and Receive for 2 UARTs, then yes, 1 MAX-232 will do the job and the space for 5 14-pin dips can be done with 1 16pin dip. I have it configured at the moment so you could install 1 1488 and 1 1489 to provide TX/RX and CTS/RTS for 2 UARTS. Let me summarize in a table (I guess I should really put this in the manual eh?) Install B3, C2, skip A2, B2, C3 = TX/RX & RTS/CTS for 2 UARTS. Install B3, C2, A2, C3, skip B2 = TX/RX, RTS/CTS & DTR/DSR for 2 UARTS and includes RI & DCD for UART 1. Install B3, C2, A2, C3, B2 = TX/RX, RTS/CTS, DTR/DSR, RI & DCD for 2 UARTS. The later RI & DCD are modem control lines, not necessary for terminals. Even DTR/DSR is not necessary for most modern terminals. On my board, I run with only B3, C2 installed. So coming back to MAX-232 question, it would have only saved space if I offered a "TX/RX for 2 UARTS" configuration, the other combinations would still require 2 to 5 MAX-232 chips. Cheers, Josh > Date: Sat, 15 Nov 2014 11:31:18 -0800 > From: ilv...@gmail.com > To: n8vem...@googlegroups.com > Subject: [N8VEM-S100:5594] S100 Serial IO Design Question > > I was sitting here staring at my 8080 CPU board and have a general question > about serial ports. I guess my question is directed at Josh but feel > free to jump in. > > Josh's board uses the 8250 (or 16550) design. The chips are large and need > the 1488 & 1489 line drivers, so require a lot of real estate especially > for two > ports. > > Could the MAX 232 serial chips have been used as an alternative? > > I think I may know the answer. Compatibility with older legacy software > and/or > desire to hold true to legacy design. > > -- > Don Caprio > ilv...@gmail.com > > -- > You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. |