terry@spcvxb.spc.edu (Terry Kennedy, Operations Mgr) (06/27/90)
In article <7cRBL1w162w@halcyon.wa.com>, ralphs@halcyon.wa.com (Ralph Sims) writes: > If it fits, it should work. The following is from Ray Gwinn's X00USER.DOC > file that comes with his device X00v122a device driver package. I generally > look to Ray for good information when it comes to this sort of thing, as > his development of the X00 driver has opened many a new avenue of data > communications. Well, let me quote from the National Semiconductor data sheet for the NS16550AF (P. 4-36 of the 1990 Data Communications/LAN/UARTs Handbook): Features: Pin for pin compatible with the existing 16450 except for CSOUT (24) and NC (29). The former CSOUT and NC pins are *TXRDY and *RXRDY, respectively. [end databook citation] The definition of CSOUT on a 16450 and earlier parts is (from P. 4-27) CSOUT: Chip Select Out Pin 24: When high, it indicates that the chip has been selected by active, CS0, CS1, and *CS2 inputs. No data transfer can be initiated until the CSOUT signal is a logic 1. CSOUT goes low when the UART is deselected. [end citation] While it is true that almost all boards do not use this signal, I have run into several that do. Such boards will not work with a 16550 without some changes. In many cases it is possible to continually assert CSOUT without harm. In others, one needs to determine which of CS0, CS1 and *CS2 are used to select the part and propagate the correct line(s), possibly through an inverter (for *CS2) or an AND gate to CSOUT. If anyone is go- ing to try this, please isolate (cut the etch) to the 16550's pins 24 and 29 first. The part gets a bit upset if you try to drive it's output lines. > A very good reference book that I use is available from National > Semiconductor Corporation. It covers most of the SIO devices > (also called UARTs) that you will find in all PCs and clones. > The title of the book is Microcommunications Elements Databook. > The publication number (manual number) is 400066. Another source of information is National Semi's Application Note AN-493, "A Comparison of the INS8250, NS16450 and NS16550AF Series of UARTs", which documents the differences between the seven versions of these parts that NS produces. It also describes (briefly) the no-suffix NS16550. This note appears on P. 4-84 of the DCom/LAN/UARTs databook I cited above... Terry Kennedy Operations Manager, Academic Computing terry@spcvxa.bitnet St. Peter's College, US terry@spcvxa.spc.edu (201) 915-9381