Inside Surfer.txt

Programming docs for the Silversurfer serial port



This document is freely distributable as long as it is not changed, and one

of the sources www.jschoenfeld.com, www.jschonfeld.de, www.siliconsonic.com

is mentioned. 



last update: March 1st, 2001



The silversurfer serial port uses a 16c550 UART Chip by California

Microdevices (www.calmicro.com). The datasheet is not available on

the internet, if you are interested in timing details, contact me directly,

as Calmicro has discontinued the part, and is no longer supporting developers

with datasheets. The UART is compatible with the common 16c550

implementations, so you may not need the details. Just to be complete:

The full part number is CM16C550PE. CM is Calmicro's prefix, and PE marks the

package (PLCC-44 in this case). 



There is somebody on the internet who claims to have developed the

Silversurfer. He gives technical information without any background, and

claims that the datasheet is available on www.cmd.com. Please do not disturb

the guys from CMD, as this is a storage company, they never made chips like

the 16c550. This is just the proof that the guy is lying - he may do good

software, but nothing else.



The silversurfer is available in two versions. The basic version is meant for

the clock-port of the A1200. The 16c550 has eight registers, and some

multiplexed registers for the Baud Rate generator. The address space for the

clock-port is 16 bytes, and the Silversurfer occupies all of them. The upper

eight registers are mirrors of the lower eight registers. In the following

text, I will only talk about the lower eight addresses, but you must keep in

mind that there may be a mirror. I'm using the term "may be" because you have

the possibiliy to disable one of the two blocks by closing a jumper (see

further down).



The second version is the "limited Edition", which has a different connector,

and a different memory map when connected to the 26-pin expansion port. When

connected to the clock-port (with a cable!), the memory map is the same as

with the standard version.



summary of registers:

(note: DLAB is short for Divisor Latch Access Bit, it's bit#7 in register#3)



Number: 0

Address in A1200: $d80001

Address on Limited Edition: Board Offset + port offset + $18



With DLAB=0:

Reading reads the "receiver Buffer Register"

Writing writes to the Transmitter holding register

With DLAB=1:

Divisor Latch (lower significant byte)



Number: 1

Address in A1200: $d80005

Address on Limited Edition: Board Offset + port offset + $1a



With DLAB=0:

interrupt enable register

With DLAB=1:

Divisor Latch (most significant byte)



The following registers are not affected by the DLAB bit:



Number: 2

Address in A1200: $d80009

Address on Limited Edition: Board Offset + port offset + $1c

read: Interrupt identification register

write: Fifo Control register



Number: 3

Address in A1200: $d8000d

Address on Limited Edition: Board Offset + port offset + $1e

Line control register



Number: 4

Address in A1200: $d80011

Address on Limited Edition: Board Offset + port offset + $38

Modem control register



Number: 5

Address in A1200: $d80015

Address on Limited Edition: Board Offset + port offset + $3a

Line status register (read only)



Number: 6

Address in A1200: $d80019

Address on Limited Edition: Board Offset + port offset + $3c

Modem status register



Number: 7

Address in A1200: $d8001d

Address on Limited Edition: Board Offset + port offset + $3e

Scratch pad register

------



With an IRQ enabled, the Silversurfer will issue an IRQ6, no matter where

it is connected. There are no more registers than the chip registers. All

you need is eight addresses.



The Z4 zorro expansion for A1200 computers has four clock-ports. It

is advisable to support them, as many people have bought the Silversurfer

because of the compatibility to this extension:



Add $4000 to all clock-port registers to access a Silversurfer on

clock-port 1 of the Z4 board. 



Add $8000 to all clock-port registers to access a Silversurfer on

clock-port 2 of the Z4 board. 



Add $c000 to all clock-port registers to access a Silversurfer on

clock-port 3 of the Z4 board.



Check for presence of the Z4 board by checking mirrors of the scratch pad

register. If you write to the scratch pad register at $d8001d and also find

that value at $d8401d, there can be no Z4 board. DO CROSS-CHECKS by writing

the scratch pad register in $d8401d and reading it back on $d8001d, as there

can be trash in the scratch pad from the previous run of your (or other)

software. Writes should be done with different bit-patterns in order to

minimize the possiblity of false identification.



Silversurfer on other clock-ports:



The Buddha Flash also contains a clock-port. This port is located at even

addresses, so substract $d80001 from the clock-port values and add the board

offset plus the port offset. In other words, if the Buddha is located at

$ea0000, the eight registers are at:



$ea0e00

$ea0e04

$ea0e08

$ea0e0c

$ea0e10

$ea0e14

$ea0e18

$ea0e1c



Similar calculation with the X-Surf clock-ports. Mind that one of the

ports uses even addresses, and the other uses odd addresses. This has

been done in order to balance the load on the data lines a bit. While

implementing software for other ports, also look at the Inside_ISDN.txt

file for the port location on the ISDN Surfer Zorro board.



The UART is clocked at 7,372800 Mhz. The frequency may sound odd, but

it is perfect for generating the common baud rates. To operate properly,

the Baud rate generator uses a 16x clock rate, so if you want to set 38400

baud, the Baud rate generator must be programmed to genberate a 614400 clock.

This is done by calculating 7372800/614400=12. Write this value to the

Divisor Latch LSB, and a 0 to the Divisor Latch MSB, and you're done.



Solder-jumpers on the back of the silversurfer:



There are six unused pads on the back of the board. Four of them are

maent for pullup/pulldown resistors or noise reduction capacitors. This

relates to my experience with the non-working Hypercom 1 models, that could

have been debugged with 33pF capacitors on IOR and IOW (unfortunately,

somebody decided to use standard low-cost capacitors, so the bug still

exists - it will not if you use X7R capacitors in SMD style!). The chip

used on the Silversurfer does not need this kind of debugging, it has a

built-in input hysteresis, so noise is filtered on-chip. Just leave the

four pads on the Silversurfer unused, and focus on the other two, which

are more interesting: They are simple jumpers, either use a wire or a 0-ohm

resistor to close the jumpers.



Never close both jumpers at the same time!



location of the jumpers:

The diagram shows the silversurfer from the solder-side!



---------------------------

|     clock-port          |

|                         |

|                         |

|                         |

|                         |

------                    -------

     |                          |

     |            1#  #3        |

     |                          |

     |            2#  #4        |

     |                          |

     |                          |

     |                      #  #|

     |                          |

     |     #  #             #  #|

     |                          |

     |     #  #                 |

     |                          |

     |                          |

     |                          |

     |                          |

     |                          |

     |                          |

     |                          |

     |                          |

     |##                        |---

     |##                        |---

     |##                        |---   serial connector

     |##                        |---

     |                          |---

     ----------------------------



Only use pads with numbers, leave the other pads (marked with #) unused!!



Usually, the CS2 signal (pin 16) of the UART is pulled high with a resistor

that is located on the top of the silversurfer. Closing one of the jumpers

applies address line A5 to this pin, either inverted, or double-inverted

(that is, directly). As a result, one of the register banks will be disabled:



Connection 1-2 (R2) will disable the lower register bank

This means, that the UART chip is only located at addresses $d80021 and up

(Mirror on $d80001 and up is free, can be used for other hardware).



Connection 3-4 (R4) will disable the upper register bank

This means, that the UART chip is only located at addresses $d80001 and up

(Mirror on $d80021 and up is free, can be used for other hardware).



These solder-jumpers are also present on the limited edition of the

Silversurfer. Only use them if you are using the clock-port connector,

otherwise you will cause even more confusion with the registers of the

26-pin connector. 



The other unused pads on the opposite side are meant for direct connection of

a DB9-male connector. This has never been used, and will only fit if you

use the Silversurfer on a Zorro board (or in a completely different

enviroment). The orientation of the connector is obvious: Four pins on the

solderside, five pins on the component side will speak for themselves. 



If you have any comments or want to have a hardcopy of the California

Microdevices datasheet, send me an e-mail: jens@jschoenfeld.de

---EOF