Differences between Z8S180 chips.

[Juha Immonen]

I had problems with ASCI communication: All worked perfectly with one 10 MHz MPU,  Z8S18010VSGZ, but not with another  Z8S18010VSGZ. I connected the /DCD0 to GND and 

/CTS0 to logic low by connecting the respective MAX232 pin to VCC. After that, all my 3 different Z8S180 MPUs  started to work fine. But one difference still remains: I was able to program my "original" Z8S18010VSGZ  to give 144000 baud rate. That I accomplished  by programming ASEXT0 register with 01101110b to get the BRG mode but not clock mode (synchronous).  CNTLB0 I programmed with 00000000b giving baud divisior 16. I also programmed the BRG Time Constant TC, setting ASTC0L and ASTC0H  both 0 to get a divisor TC+2=2. SO I got Baud rate = 9216000/(32*(TC+2)) = 144000. But that doesn't work with my Z8S18010VSC.

Any ideas?

Thanks, Juha

[Bill McMullen]

I'd suggest you read Zilog's TN0053 application note that can be found here: https://www.zilog.com/docs/z180/appnotes/TN0053.pdf

Since you're obviously working with remarked Z180's, it's not obvious whether you're working with a revised later version or an earlier SL1960 variant.  Often the first indicator of an issue is that the SL1960 variants do not have a clock doubler option which can manifest itself as different baud rates when using the original method of setting the baud rate.  Perhaps you can try write then read back the BRG register since the SL1960 variant does not have those registers and likely will not return the written value.