POKE_L

Syntax

POKE address,value or

POKE address, value1 *[,valuei]*(Minerva and SMS only) or

POKE address, {value1 | value1$} *{,valuei | valuei$}* (SMS only)

and

POKE_W address,value or

POKE_W address, value1 *[,valuei]*(Minerva and SMS only)

and

POKE_L address,value or

POKE_L address, value1 *[,valuei]*(Minerva and SMS only)

Location QL ROM

Both kinds of internal memory (RAM and ROM) are organised as a stream of values. The basic unit for memory is a bit (a value of 0 or 1 relating to false or true), which relates to the binary system of counting.

Eight bits are combined to form a byte (0 to 255), sixteen bits make a word, and thirty-two a longword. Words and longwords are signed whilst bytes are unsigned.

The POKE commands allow you to set values in memory.

It is however unwise to POKE just anywhere, because there could be important code present in that part of memory which will be disrupted by POKEs and could crash your computer. You would generally have already set aside a part of memory for use by your own programs, by using RESPR or ALCHP and then you would POKE different values in that part of memory, eg. for storing data. This is a representation of the relationship between bits, bytes, words and longwords:

Bits 10011000 10001000 11011111 10111000
Bytes 152 136 223 184
Words -26488 -8264
Long Word -1.73586E9

or

Bits 01110110 11000111 01100000 00000011
Bytes 118 199 96 3
Words 30407 24579
Long Word 1.992778E9

NOTE 1

Negative values can also be stored in memory. However, they are stored by deducting the number from the maximum number which can be stored in a byte plus one.

POKE 131072,255
POKE 131072,-1

have the same effect.

NOTE 2

Do not try to POKE_W or POKE_L to an odd address (eg. 10001) as this will cause an error unless you are using Minerva (see below).

NOTE 3

If you try to poke a value which is too big to fit into the given space, eg:

POKE 131072, -32768

then only the least significant byte is used (with POKE) and the low word is used (with POKE_W).

NOTE 4

The THOR XVI limits value to the following ranges: POKE: -128..255; POKE_W: -32768..65535

MINERVA NOTES

The POKE, POKE_W and POKE_L commands on Minerva (version 1.77 or later) are very much enhanced and different. Minerva allows you to POKE_W and POKE_L to odd addresses. eg:

POKE_W 131073,100100

Minerva has also added to the usefulness of the POKE, POKE_W and POKE_L commands by allowing them to store a list of numbers in one go.

As an example the following two program lines have exactly the same effect, although only line 100 will run on a non-Minerva QL.

100 POKE_W start,10: POKE_W start+2,125: POKE_W start+4,10322
110 POKE_W start,10,125,10322

Minerva also allows the BASIC programmer to access the QL’s SuperBASIC variables, system variables and Minerva’s own System Xtensions (although the extended PEEKs should be of more use). You will need a good book on QDOS (eg. QDOS/SMS Reference Manual) to find out what the possible values are. The syntax for these extra commands is:

Alter SuperBASIC variables

POKE \\SBvar,value: REMark SBvar=0...256
POKE_W \\SBvar,value
POKE_L \\SBvar,value
POKE \SBvar\Offset,value
POKE_W \SBvar\Offset,value
POKE_L \SBvar\Offset,value

Alter System variables

POKE !!Sysvar,value: REMark Sysvar=0...1152
POKE_W !!Sysvar,value
POKE_L !!Sysvar,value
POKE !Sysvar!Offset,value
POKE_W !Sysvar!Offset,value
POKE_L !Sysvar!Offset,value

The command

POKE \\SBvar,value

will alter the SuperBASIC variable pointed to by Sysvar, such as the current line number. The most useful of these are variables $68 onwards.

The command

POKE \SBvar\Offset,value

allows you to alter the different SuperBASIC tables used by the QL (eg. the channel table). The start addresses of the different tables are contained in the SuperBASIC variables $0 to $64. SBvar must contain the relevant SuperBASIC variable (the pointer to the required table), then the Offset is the required address within the table.

The command

POKE !!Sysvar,value

allows you to alter the different system variables (normally stored at $28000 on a QL, but they can move!). These are useful for accessing the current network number, finding free space, accessing device drivers, forcing <CAPSLOCK>….. Sysvar merely contains the number of the required system variable.

The command

POKE !Sysvar!Offset,value

takes the address contained within the given system variable, adds the Offset to that address and then pokes it with the given value.

On a Minerva machine the system variable stored at $7C (124) (SV.CHTOP) contains the address of the Minerva System Xtensions, therefore to alter these:

SysX = PEEK_L (ver$(-2) + 124)
POKE SysX + offset,value
POKE_W SysX + offset,value
POKE_L SysX + offset,value

Minerva’s System Xtensions provide such things as the addresses for translation tables, the attributes for the size type and colour of a cursor, the fonts for all subsequently opened windows and much more… (see Minerva manual for list).

Minerva Example 1

It is sometimes useful to alter the key repeat delay and frequency to make allowances for when a different keyboard is attached to the QL, so that you can type more quickly without having the problem that you are waiting around for auto-repeat to take effect. These two values can now simply be altered using:

POKE_W !!140, key_delay
POKE_W !!142, key_frequency

Minerva Example 2

Want to attach a new font to all channels which will be opened in the future?

100 a=RESPR(2000)
110 LBYTES flp1_new_font, a
120 POKE_L !124!40, a

Minerva Example 3

It might be useful in an error trapping routine to find the current DATA position (eg. if there is an error when reading data into a variable), so that the position may be returned to later once the error has been overcome. You may even wish to miss out the problem DATA line. This program is an ‘intelligent’ data-loader:

100 WHEN ERRor
110 data_line=PEEK_W(\\148)
115 PRINT 'ERROR IN DATA LINE'!data_line!';statement'! PEEK(\\151)-1
120 INPUT 'Go to next data line (y/n)'!a$
130 IF a$=='y': POKE_W\\148,data_line+1: POKE\\150,1:POKE\\151,1: RETRY
140 IF a$=='n' THEN
145   data_store=PEEK_W(\\148)*65536+(PEEK(\\150)-1)*256+PEEK(\\151)-1
147   PRINT"Alter offending line then enter re_run":STOP
149 END IF
150 END WHEN 155 :
160 RESTORE
170 ax=RESPR(100):i=0
180 REPeat data_load
190   IF EOF: EXIT data_load
200   READ b
210   PRINT b,i:POKE ax+i,b
220   i=i+1
230 END REPeat data_load
240 DATA 10,10,2,3,3a,10
250 DATA 10,2,2,3,3,2
255 :
260 DEFine PROCedure RE_run
270   POKE_L \\148,data_store: GO TO 170
280 END DEFine

SMS NOTE

POKE, POKE_W and POKE_L have been made the same as on Minerva except that POKE_W and POKE_L cannot address odd addresses.

SMS does not possess Minerva’s System Xtensions.

Please also note that SMS’s improved interpreter won’t allow you to enter line 240 in the Minerva Example 3 as the data item 3a will be rejected.

One extra addition to SMS is that the POKE command can actually accept a string as a value to be poked into memory. If a string is passed as a parameter, each character of the string is converted to its character code and then that byte poked into memory, for example:

POKE base,0,5,'WIN1_'

will store ‘WIN1_’ as a standard QL string (a word containing its length followed by the string itself) at the address in memory pointed to by base. Note that if you pass an empty string, this will have no effect.

WARNING

If you are POKEing around in memory then make sure that you know what you are doing.

On every QDOS machine, even RAM areas which have not been set aside for program use are used by the operating system, eg. for buffering purposes. On Emulators and QLs fitted with a Gold Card, the operating system itself is no longer in ROM but is moved into RAM. POKEing in this area will almost surely lead to crashes. Even advanced users who know which parts of memory are used by QDOS should avoid amending QDOS directly. There are more elegant and safer methods how to do this which will run on every QDOS compatible computer.

CROSS-REFERENCE

PEEK, PEEK_W, PEEK_L and PEEK$ read memory values and POKE$ is another command to set them. CHAR_DEF allows you to attach a font to all channels OPENed after the command. POKES allows you to POKE memory in Supervisor mode.